Regenerable sulfur traps for on-board vehicle applications

ABSTRACT

Provided are improved exhaust gas cleaning systems and methods for treating exhaust gas from a combustion source that include a hydrogen generation system, a regenerable sulfur oxides trap, and a regenerable nitrogen storage reduction (NSR) catalyst trap. The improved exhaust gas cleaning systems and methods allow for the sulfur released from the sulfur trap to pass through the nitrogen oxide trap with no or little poisoning of NO x  storage and reduction sites, which significantly improves NSR catalyst trap lifetime and performance to meet future emissions standards. The disclosed exhaust gas cleaning systems are suitable for use in internal combustion engines (e.g., diesel, gasoline, CNG) which operate with lean air/fuel ratios over most of the operating period.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.12/082,351, filed Apr. 10, 2008 which claims the benefit of U.S.Provisional Application No. 60/922,844 filed on Apr. 11, 2007, and whichis a Continuation-in-Part of U.S. application Ser. No. 11/179,372 filedon Jul. 12, 2005, all of which are herein incorporated by reference.

FIELD

The present disclosure relates to the field of exhaust gas cleaningsystems for combustion engines. It more particularly relates to animproved process for operating an exhaust gas treatment unit consistingof a hydrogen rich gas source, a sulfur (SO_(x)) catalyst trap and anitrogen oxide (NO_(x)) storage reduction (NSR) catalyst trap. Stillmore particularly, the present disclosure relates to a process based onusing a H₂ gas rich to enable the sulfur released from the sulfur(SO_(x)) trap to pass through a NO_(x) storage reduction (NSR) catalysttrap with no poisoning of the NO_(x) storage and reduction components.Still yet more particularly, the present disclosure relates to improvedSOx trap compositions that adsorb SOx as metal sulfates under leanexhaust conditions and desorb accumulated SOx by reduction of metalsulfate under rich exhaust conditions.

BACKGROUND

In Japan, the NO_(x) storage reduction (NSR) catalyst also known asNO_(x) trap or NO_(x) adsorbent is a demonstrated after treatmenttechnology for control of HC, CO, and NO_(x) on vehicles equipped withlean burn gasoline engines. This catalyst provides two key functions.When the engine operates with a stoichiometric air/fuel ratio, itfunctions as a standard three-way conversion catalyst. Under leanoperating conditions, while CO and HC in the exhaust are combusted, theNSR catalyst trap functions as a trap for NO_(x) (NO+NO₂). The reactionmechanism of NO_(x) storage and reduction over a NSR catalyst trap aredepicted in Equations 1-4. In general, a NSR catalyst trap shouldexhibit both oxidation and reduction functions. In a lean environment,NO is oxidized to NO₂ (Equation 1). This reaction is catalyzed by anoble metal (e.g., Pt). Further oxidation of NO₂ to nitrate, withincorporation of an atomic oxygen occurs. The nitrate is then storedover selected metal components (Equation 2). To ensure continuous andlasting NO_(x) control, the NSR catalyst trap requires periodicregeneration with controlled short, rich pulses, which serve to release(Equation 3) and reduce the stored NO_(x) (Equation 4). Again a Pt groupmetal is used for NO_(x) release and reduction. Poisoning of the NSRcatalyst trap by sulfur oxides takes place in principle in the same wayas the storage of nitrogen oxides. The sulfur dioxide emitted by theengine is oxidized to sulfur trioxide on the catalytically active noblemetal component (e.g., Pt) of the NSR catalyst trap (Equation 5). Sulfurtrioxide (SO₃) reacts with the storage materials (e.g., Ba) in the NSRcatalyst trap with the formation of the corresponding sulfates (Equation6). Because of the low capacity of the trap to hold sulfur beforeactivity falls and of the stability of sulfate poisons, frequent hightemperature desulfations under fuel rich conditions are required (>650°C.). This stresses the thermal stability of the NSR catalyst trap andultimately results in a significant fuel penalty as a result of runninga fuel rich mixture as required for high temperature desulfations. Thiscorrespondingly shortens NSR catalyst trap life.

Equations:NO+1/2O₂=NO₂ Oxidation of NO to NO₂  (1)2NO₂+MCO₃+1/2O₂=M(NO₃)₂+CO₂NO_(x) Storage as Nitrate   (2)M(NO₃)₂+2CO=MCO₃+NO₂+NO+CO₂NO_(x) release:   (3)NO+NO₂+3CO=N₂+3CO₂NO_(x) reduction to N₂   (4)SO₂+1/2O₂=SO₃SO_(x) poisoning Process   (5)SO₃+MCO₃=MSO₄+CO₂SO_(x) poisoning Process   (6)

In equations 2, 3 and 6, M represents a divalent base metal cation(e.g., Ba). M can also be a monovalent or trivalent metal compound, inwhich case the equations need to be rebalanced.

One method for decreasing the formation of sulfates that poison the NSRcatalyst trap is to provide a SO_(x) trap upstream of the NSR catalysttrap which undergoes a continuous sulfur uptake and release as afunction of the air/fuel ratio (A/F ratio). By periodically changing theexhaust gas conditions from lean to rich, the sulfates stored on sulfurtrap are decomposed to yield sulfur species, and the nitrates stored onthe NSR catalyst trap are reduced to nitrogen. Key requirements are thata substantial fraction of sulfur species released pass through the NSRcatalyst trap with no poisoning of the NO_(x) storage (e.g., Ba) andreduction components (e.g., Pt).

EP 0582917 A1 discloses that the poisoning of a storage catalyst withsulfur can be reduced by a sulfur trap inserted into the exhaust gasstream upstream of the storage catalyst. Alkali metals (potassium,sodium, lithium and cesium), alkaline earth metals (barium and calcium),and rare earth metals (lanthanum and yttrium) are disclosed as storagematerials for the sulfur trap. The sulfur trap also includes platinum(Pt) as a catalytically active component. However the disadvantage ofthe embodiments in EP 0582917 A1 is that the sulfur storage capacity islimited, unless an inordinately large trap is provided or the trap isreplaced at very frequent intervals. Once the sulfur trap reaches itsfull storage capacity sulfur oxides contained in the exhaust gas willpass through the sulfur trap and poison the NSR catalyst trap.

EP 0625633 discloses an improvement to the design disclosed in EP0582917 by also providing a sulfur trap just upstream of the NSRcatalyst in the exhaust gas stream of the internal combustion engine.The combination of sulfur trap and NSR catalyst is operated in such waythat sulfur oxides are stored on the sulfur trap and nitrogen oxides arestored on the NSR catalyst under lean exhaust conditions. Byperiodically changing the exhaust gas conditions from lean to rich, thesulfates stored on sulfur trap are decomposed to yield sulfur dioxide,and the nitrates stored on the NSR catalyst are decomposed to yieldnitrogen dioxide. EP 0625633 also discloses a further improvement byhighly enriching the exhaust gas to release nitrogen oxides from thenitrogen oxide catalyst and only slightly enriching the exhaust gas torelease the sulfur oxides from the sulfur oxide trap. The quantities ofsulfur oxides contained in the exhaust gas from an internal combustionengine are much smaller than the quantities of nitrogen oxides, andtherefore, it is not necessary to also remove sulfur from the sulfuroxide trap each time the nitrogen oxides are released from the storagecatalyst. The period of the cycle for releasing nitrogen oxides from theNSR catalyst is about one minute, whereas the period for releasing fromthe sulfur trap is several hours according to EP 0582917.

U.S. Pat. No. 5,473,890 discloses a SO_(x) trap composition selectedfrom alkali, alkali-earth, and rare earth metals. Pt is also added tothis formulation. High temperature regeneration (>650° C.) is needed forsuch a system, which is not a practical solution since this will resultin thermal damage to this trap and the NSR unit in the same flow line,which is also shown operated in the same flow line at this temperature.U.S. Pat. No. 5,473,890 refers to a SO_(x) trap containing at least onemember selected from copper, iron, manganese, nickel sodium, titanium,lithium and titania. In addition Pt is added to the catalyst. Ptcontaining adsorbents result in significant quantities of H₂S releaseunder rich conditions, which will react with sulfur trap componentsforming stable metal sulfide leading to only a partial regeneration ofSO_(x) trap. The authors did not show any test activity for the system.

U.S. Pat. No. 5,687,565 discloses a very complex oxide composition,selected from alkaline earth oxides (Mg, Ca, Sr, Ba, Zn). In addition Cuand noble metals (Pt, Pd, Ru) were also added. Again such a system isunpractical as a regenerable SO_(x) trap due to the need for 650°C.+regeneration and the poisoning effects of H₂S release.

U.S. Pat. No. 5,792,436 discloses SO_(x) traps containing alkaline earthmetal oxides selected from Mg, Ca, Sr, Ba in combination with oxides ofcerium and a group of elements of atomic numbers from 22 to 29. Pt isalso added to the catalysts formulation. Again such a system requireshigh temperatures to regenerate (>650° C.).

EP 1374978 A1 discloses SO_(x) traps containing oxides of copper. Theauthors indicate that the system can be regenerated at low temperature(250-400° C.) depending on the support. However, the authors did notshow any data on the effect of the released sulfur species (e.g., SO₂)on NSR catalyst trap. As will be discussed later, the released SO₂ atthese low temperatures will poison NSR reduction sites under richconditions.

U.S. Pat. No. 6,145,303 discloses H₂S formation under rich conditions,and a method to suppress it when the air/fuel ratio is close tostoichiometry. This approach to suppress H₂S formation translates into apartial and a long regeneration period of the sulfur trap. Moreover, ahigher temperature is needed for desulfation, which can also stress thethermal stability of the sulfur trap.

WO 0156686 discloses that the release of sulfur under rich conditionsleads to the adsorption of sulfur species on NSR. Also disclosed is thatsuch sulfur adsorption will affect the NSR catalyst trap and a hightemperature desulfation procedure of the NSR catalyst trap is needed.

The aforementioned methods for operating an exhaust gas treatment unitconsisting of a sulfur trap and a nitrogen oxides storage reductioncatalyst have two distinct disadvantages. The first disadvantage is theabsence of a procedure to transmit sulfur species through NSR catalysttrap with no poisoning of NO_(x) storage and reduction sites. The seconddisadvantage is that most of the reported sulfur traps contain Pt andare partially regenerated at high temperatures releasing H₂S as mainproduct. In addition H₂S may be an issue for future regulation and needsto be controlled.

A need exists for an improved process for operating an exhaust gastreatment unit including a sulfur trap and a NSR catalyst trap operatedin tandem. The system will ideally have a SO_(x) trap regenerable atmoderate temperatures (˜400-600° C.) by use of a regeneration gas mediathat can enable the sulfur species released from sulfur trap to passthrough the NSR catalyst trap with no poisoning of NO_(x) storage andcatalytic components. A need also exists to further optimize thecatalyst and catalyst support materials for use in the sulfur trap toprovide broader operating windows during SO_(x) adsorption anddesorption.

SUMMARY

Provided are sulfur trap compositions, exhaust gas cleaning systems andmethods for treating exhaust gases from a combustion source. Moreparticularly, provided are methods for passing sulfur species (e.g. SO₂,H₂S, COS or mixture formed during regeneration of SOx trap) through aNSR catalyst without, or with minimal poisoning of NSR catalyst sites(e.g. Pt and BaCO₃ sites) under rich conditions at a controlledtemperature window (e.g. 400 to 575° C.) and in presence of controlledamount of H₂.

According to one aspect of the present disclosure, a regenerable sulfuroxides trap catalyst composition for trapping SO_(x) from a combustionsource comprises a metal (M) oxide/support, wherein M is selected fromCu, Fe, Mn, Ag, Co, Ce, Zr and combinations thereof, and wherein themetal oxide is on a catalyst support (S), wherein S is selected from anoxide of alumina, stabilized gamma alumina with rare earth components,MCM-41, zeolites, silica, magnesium, zirconia, ceria, ceria-zirconia,titania, titania-zirconia, and combinations thereof.

Another aspect of the present disclosure relates to a regenerable sulfuroxides trap catalyst composition for trapping SO_(x) from a combustionsource comprising a mixed metal (M)-La—Zr oxide, wherein M is selectedfrom Cu, Fe, Mn, Ag, Co, Ce and combinations thereof.

Another aspect of the present disclosure relates to a regenerable sulfuroxides trap catalyst composition for trapping SO_(x) from a combustionsource comprising a metal oxide, wherein the metal oxide is selectedfrom Ce—Zr oxide, Ce—Fe oxide Pt—Ba oxide, and combinations thereof.

A further aspect of the present disclosure relates to an exhaust gascleaning system for a combustion source comprising: a) a H₂ rich gasgenerator system, b) a regenerable sulfur oxides trap, and c) aregenerable nitrogen storage reduction (NSR) catalyst trap, wherein thesulfur oxides trap comprises a catalyst selected from Ce—Zr oxide, Ce—Feoxide, Mn—La—Zr oxide, Fe—La—Zr oxide, Cu—La—Zr oxide, Co—La—Zr oxide,Pt—Ba oxide, Pt, and combinations thereof, wherein the NSR catalyst trapis positioned downstream of the sulfur oxides trap and the H₂ rich gasgenerator system, wherein the sulfur oxides trap releases sulfur atomspecies during regeneration under a rich fuel to air ratio condition tothe downstream NSR catalyst trap, wherein the NSR catalyst trap is at atemperature of from about 400 to about 600° C. in the presence of H₂from the H₂ rich gas generator system, and at an atomic ratio of H₂ tothe released sulfur atom species of greater than or equal to about 65during regeneration of the sulfur oxides trap, and wherein the sulfuratom species released by the sulfur oxides trap pass through the NSRcatalyst trap with no poisoning of the NO_(x) storage and NO_(x)reduction components.

Still another aspect of the present disclosure relates to a method forimproving the treatment of exhaust gas comprising the steps of: i)providing a combustion source with an exhaust gas cleaning systemcomprising: a H₂ rich gas generator system, a regenerable sulfur oxidestrap, and a regenerable nitrogen storage reduction (NSR) catalyst trap,wherein the sulfur oxides trap comprises a catalyst selected from Ce—Zroxide, Ce—Fe oxide, Mn—La—Zr oxide, Fe—La—Zr oxide, Cu—La—Zr oxide,Co—La—Zr oxide, Pt—Ba oxide, Pt, and combinations thereof, wherein theNSR catalyst trap is positioned downstream of the sulfur oxides trap andthe H₂ rich gas generator system, and ii) regenerating the sulfur oxidestrap and the NSR catalyst trap with the H₂ rich gas and reductant richexhaust generated by operation of the engine at greater than thestoichiometric fuel/air ratio, and iii) maintaining the NSR catalysttrap at a temperature of from about 400 to about 600° C. in the presenceof H₂ from the H₂ rich gas generator system at an atomic ratio of H₂ tothe released sulfur atom species of greater than or equal to about 65during regeneration of the sulfur oxides trap, wherein the sulfur atomspecies released by the sulfur oxides trap pass through the NSR catalysttrap with no poisoning of the NO_(x) storage and NO_(x) reductioncomponents.

Numerous advantages result from the advantageous regenerable sulfur trapcatalyst compositions, exhaust gas cleaning systems and methods forimproving the treatment of exhaust gas disclosed herein and theuses/applications therefore.

For example, in exemplary embodiments of the present disclosure, thedisclosed exhaust gas cleaning system comprising a regenerable sulfurtrap, a hydrogen source, and an NSR catalyst trap exhibits that sulfurreleased from the sulfur trap subsequently passes through the NSRcatalyst trap in presence of low amount of H₂ with no poisoning ofNO_(x) storage and reduction components.

In a further exemplary embodiment of the present disclosure, thedisclosed exhaust gas cleaning system comprising a regenerable sulfurtrap, a hydrogen source, and an NSR catalyst trap exhibits improveddurability of the NSR catalyst trap when positioned downstream of asulfur trap.

In a further exemplary embodiment of the present disclosure, thedisclosed exhaust gas cleaning system comprising a regenerable sulfurtrap, a hydrogen source, and an NSR catalyst trap exhibits the abilityto regenerate both the sulfur trap and the NSR catalyst trap at atemperature below 600° C. while avoiding thermal stress of the catalystand the fuel penalty.

In a further exemplary embodiment of the present disclosure, thedisclosed exhaust gas cleaning system comprising a regenerable sulfurtrap, a hydrogen source, and an NSR catalyst trap exhibits improved NSRcatalyst lifetime and performance.

In a further exemplary embodiment of the present disclosure, thedisclosed exhaust gas cleaning system comprising a regenerable sulfurtrap, a hydrogen source, and an NSR catalyst trap further includes ashift converter (water gas shift (WGS) catalyst) of improved catalystcomposition to efficiently convert carbon monoxide to carbon dioxide andhydrogen without need for special catalyst reconditioning.

In a further exemplary embodiment of the present disclosure, thedisclosed exhaust gas cleaning system comprising a regenerable sulfurtrap, a hydrogen source, and an NSR catalyst trap includes a WGScatalyst of improved composition having increased activity in a shiftconversion reactor for converting carbon monoxide to carbon dioxide andhydrogen without need to protect the WGS catalyst from lean conditions.

In a further exemplary embodiment of the present disclosure, thedisclosed exhaust gas cleaning system comprising a regenerable sulfurtrap, a hydrogen source, and an NSR catalyst trap includes a WGScatalyst of improved catalyst composition providing for improvedactivity and durability over existing catalyst for the water-gas-shiftreaction.

These and other advantages, features and attributes of the disclosedregenerable sulfur trap compositions, exhaust gas cleaning systems andmethods for treating exhaust gases from a combustion source of thepresent disclosure and their advantageous applications and/or uses willbe apparent from the detailed description which follows, particularlywhen read in conjunction with the figures appended hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

To assist those of ordinary skill in the relevant art in making andusing the subject matter hereof, reference is made to the appendeddrawings, wherein:

FIG. 1 depicts an illustrative schematic of a treatment unit for theexhaust gas from an engine according to the present disclosure. Theexhaust gas treatment unit includes a H₂ rich gas generator system (1),a SO_(x) trap (2) downstream of the H₂ generator system (1), and a NSRcatalyst trap (3) downstream of the SO_(x) trap (2).

FIG. 2 depicts an illustrative schematic of a treatment unit for theexhaust gas from an engine with the only difference from FIG. 1 beingthat that the rich gas H₂ generator system (1) is positioned downstreamof the SO_(x) trap (2) and upstream of the NSR catalyst trap (3).

FIG. 3 depicts an illustrative schematic of an exhaust gas purifyingsystem for an internal combustion engine having a H₂ rich gas generationsystem (1) and the 3 catalyst systems (sulfur trap (2), awater-gas-shift (WGS) catalyst (2′), and a NSR catalyst trap (3)). Theonly difference from FIG. 1 is that a WGS catalyst (2′) is addedupstream of the NSR catalyst trap (3).

FIG. 4 depicts an illustrative schematic of an exhaust gas purifyingsystem for an internal combustion engine, according to the presentdisclosure, having a H₂ rich gas generator system (1) and the 3 catalystsystems (sulfur trap (2), a WGS (2′), a NSR catalyst trap (3)), andadditionally a clean-up trap/catalyst (4).

FIG. 5 depicts a graphical illustration of the NO_(x) reduction at 450°C. over a NSR catalyst trap under simulated rich conditions containingC₃H₆/CO in the presence (Feed 2 a, Table 1) and absence (Feed 1,Table 1) of sulfur species and with no H₂.

FIG. 6 depicts a graphical illustration of the effect of SO₂ on NO_(x)reduction at 450° C. over a NSR catalyst trap under simulated richconditions containing H₂ (Feed 2 b, Table 1).

FIG. 7 depicts a graphical illustration of the effect of H₂S on NO_(x)reduction at 300° C. and 450° C. over a NSR catalyst trap undersimulated rich conditions containing H₂ (Feed b, Table 1).

FIG. 8 depicts a graphical illustration of the effect of H₂S on NO_(x)reduction at 300° C. over a NSR catalyst trap under simulated richconditions containing C₃H₆/CO (Feed a, Table 1).

FIG. 9 depicts a graphical illustration of NO_(x) storage (Feed 4,Table 1) at 300° C. following 1 cycle poisoning by SO₂ under simulatedrich conditions containing C₃H₆/CO (Feed 2 a) and oxidation (Feed 3,Table 1) at 450° C. of the adsorbed SO₂.

FIG. 10 depicts a graphical illustration of NO_(x) storage (Feed 4) at300° C. over a NSR catalyst trap following 1 and 5 cycles poisoning byH₂S under simulated rich conditions containing C₃H₆/CO (Feed 2 a,Table 1) and oxidation (Feed 3, Table 1) at 450° C. of the adsorbed H₂Sbetween each cycle.

FIG. 11 depicts a graphical illustration of NO_(x) storage (Feed 4) at300° C. over a NSR catalyst trap following 1 and 5 cycles poisoning bySO₂ under simulated rich conditions containing H₂ (Feed 2 b, Table 1)and oxidation (Feed 3, Table 1) at 450° C. of the adsorbed H₂S betweeneach cycle.

FIG. 12. depicts a graphical illustration of NO_(x) storage (Feed 4) at300° C. over a NSR catalyst trap following 1 and 5 cycles poisoning byH₂S under simulated rich conditions containing H₂ (Feed 2 b, Table 1)and oxidation (Feed 3, Table 1) at 450° C. of the adsorbed H₂S betweeneach cycle.

FIG. 13 depicts a graphical illustration of NO_(x) storage (Feed 4,Table 1) at 300° C. over a NSR catalyst trap following 1 and 5 cyclespoisoning by H₂S under simulated rich conditions containing H₂ (Feed 2b, Table 1) and oxidation (Feed 3, Table 1) at 300° C. of the adsorbedH₂S between each cycle.

FIG. 14 depicts a XRD pattern of a pretreated fresh NSR.

FIG. 15 depicts a graphical illustration of SO₂ and H₂S levels belowwhich bulk solid poisoning of the NSR catalyst trap will not occur as afunction of temperature.

FIG. 16 depicts a schematic illustrating sulfur poisoning of Pt and Basites in NSR catalyst trap when cycling from rich to lean conditions.

FIG. 17 depicts a graphical illustration of the H₂/H₂S ratio needed toavoid PtS formation as a function of temperature during regeneration ofthe SO_(x) catalyst trap.

FIG. 18 depicts a graphical illustration of the first derivative of theweight loss during the reduction of the sulfated metal-containingalumina (Metal=Cu, Fe, Co and Mn).

FIG. 19 depicts a graphical illustration of sulfur species releasedduring the reduction of sulfated Cu/Al₂O₃ of example 4 (sulfation at400° C.).

FIG. 20 depicts a graphical illustration of sulfur species releasedduring the reduction of the sulfated Fe/Al₂O₃ of example 7 (sulfation at400° C.).

FIG. 21 depicts a graphical illustration of sulfur species releasedduring the reduction of the sulfated Co/Al₂O₃ of example 6 (sulfation at400° C.).

FIG. 22 depicts a graphical illustration of sulfur species releasedduring the reduction of the sulfated Mn/Al₂O₃ of example 5 (sulfation at400° C.).

FIG. 23 depicts a graphical illustration of sulfur species releasedduring the reduction of the sulfated Ce/Al₂O₃ of example 8 (sulfation at200° C.).

FIG. 24 depicts a graphical illustration of sulfur species releasedduring the reduction of the sulfated Pt—Fe/Al₂O₃ of example 9 (sulfationat 400° C.).

FIG. 25 depicts a graphical illustration of sulfur species releasedduring the thermal decomposition in He of the sulfated Pt—Fe/Al₂O₃ ofexample 9 (sulfation at 400° C.).

FIG. 26 depicts a graphical illustration of sulfur species releasedduring the reduction of a sulfated Fe/Al₂O₃ of example 7 where anupstream Pt/Al₂O₃ of example 10 was used during sulfation (sulfation at400° C.).

FIG. 27 depicts a graphical illustration of sulfur species releasedduring isothermal reduction at 450° C. of a sulfated Fe/Al₂O₃ of example7 where an upstream Pt/Al₂O₃ of example 10 was used during leansulfation (sulfation at 400° C.).

FIG. 28 depicts a graphical illustration of sulfur species desorptionduring the reduction of the sulfated Pt—Ba/Al₂O₃ (sulfation at 400° C.).

FIG. 29 depicts a graphical illustration of sulfur species desorptionduring the reduction of the sulfated Ce—Fe/Al₂O₃ (sulfation at 200° C.).

FIG. 30 depicts a graphical illustration of sulfur species desorptionduring the reduction of the sulfated Ce—Zr/Al₂O₃ (sulfation at 200° C.).

FIG. 31 depicts a graphical illustration of sulfur species desorptionduring the reduction of the sulfated Mn—La—Zr/Al₂O₃ from example 15(sulfation at 200° C.).

FIG. 32 depicts a graphical illustration of sulfur species desorptionduring the reduction of the sulfated Mn—La—Zr/Al₂O₃ from example 15(sulfation at 400° C.).

FIG. 33 depicts a graphical illustration of sulfur species desorptionduring the reduction of the sulfated Mn—La—Zr/Al₂O₃ from example 16(sulfation at 200° C.).

FIG. 34 depicts a graphical illustration of sulfur species desorptionduring the reduction of the sulfated Mn—La—Zr/Al₂O₃ from example 16(sulfation at 400° C.).

FIG. 35 depicts NO_(x) storage efficiency under lean conditions and inthe presence of small amount of H₂ using the Ag/Al₂O₃ catalyst ofexample 11.

FIG. 36 depicts H₂ oxidation with O₂ under rich conditions in presenceand in absence of CO over the Pt/Al₂O₃ catalyst of example 10.

FIG. 37 depicts a graphical illustration of hydrogen concentrationversus temperature and Ce loading on the water gas shift reaction overRh supported CeO₂—ZrO₂ for a feed of 4% CO+17% H₂O at GHSV=14,683 h⁻¹.

FIG. 38 depicts a graphical illustration of hydrogen concentrationversus temperature and Ce loading on the water gas shift reaction overPt supported CeO₂—ZrO₂ for a feed of 4% CO+17% H₂O at GHSV=73,194 h⁻¹.

FIG. 39 depicts a graphical illustration of hydrogen concentrationversus temperature and Ce loading on the water gas shift reaction overRh supported CeO₂—ZrO₂ for a feed of 4% CO+17% H₂O at GHSV=14,683 h⁻¹.

FIG. 40 depicts a graphical illustration of average NO_(x) storage (1min average, Feed 4) at 300° C. over a NSR catalyst trap followingdifferent cycles of SO₂ poisoning under simulated rich conditionscontaining H₂ (Feed 2 b, Table 1) and oxidation (Feed 3, Table 1) at450° C. of the adsorbed SO₂ between each cycle. The GHSV was 30,000 h⁻¹.

FIG. 41 depicts a graphical illustration of average NO_(x) storage (1min average, Feed 4) at 450° C. over a NSR catalyst trap followingdifferent cycles of SO₂ poisoning under simulated rich conditionscontaining H₂ (Feed 2 b, Table 1) and oxidation (Feed 3, Table 1) at450° C. of the adsorbed SO₂ between each cycle. The GHSV was 30,000 h⁻¹.Average NO_(x) storage after 1 cycle SO₂ poisoning under lean conditions(feed 3 with 90 ppm SO₂) is also reported.

DETAILED DESCRIPTION

The present disclosure relates to an improved sulfur trap compositionsfor trapping SO_(x) from combustion sources, and their use in exhaustgas treatment systems and processes. The sulfur trap compositions aredistinguishable over the prior art in providing novel regenerablecompositions that provide broader operating windows during SO_(x)adsorption and desorption. In addition, the exhaust gas treatment systemand process disclosed herein are distinguishable over the prior art incomprising a combination of improved sulfur trap compositions (alsoreferred to herein as a sulfur oxides trap or a SO_(x) trap), a hydrogensource (also referred to herein as a hydrogen generator or generationsystem), and a nitrogen oxide trap (also referred to herein as a NO_(x)trap, NO_(x) adsorbent or NO_(x) storage reduction (NSR) catalyst) whichin combination advantageously decrease sulfur adsorption, and poisoningof the NSR catalyst trap. More particularly, the present disclosurerelates to deployment of improved sulfur trap compositions in animproved system and method for operating an exhaust gas treatment unitincluding a sulfur trap, a hydrogen source, and a NSR catalyst trap,wherein the process is based on generating H₂ on-board the vehicle toenable the sulfur released from sulfur trap (SO₂, H₂S, COS) to passthrough the NSR catalyst trap with no or little poisoning of NO_(x)storage and reduction components. The improved method for operating anexhaust gas treatment unit may also optionally include the addition of awater gas shift catalyst trap, and a clean-up catalyst trap.

The present disclosure also provides a set of SO_(x) trap compositionsthat adsorb SO_(x) under a wide range of lean conditions and desorbSO_(x) species under fuel rich conditions in presence of controlledamount of H₂ with the effluent being a compositional mixture that willpass through an NSR trap with minimal poisoning effects. Moreparticularly, provided are SO_(x) trap compositions that will onlyrelease adsorbed sulfur species under fuel rich conditions in thepresence of a controlled amount of H₂ in a compositional mixture whichwill pass through an NSR trap with minimal poisoning effects when thetemperature of the SO_(x) trap is above 400° C. The operation of thesenew SO_(x) trap compositions are provided upstream of and in combinationwith a NO_(x) trap, wherein the released gaseous mixture from the SO_(x)trap is exposed to the NO_(x) trap at a controlled temperature window(400-575° C.).

The present disclosure also relates to methods for passing sulfurspecies (SO₂, H₂S, COS or mixture formed during regeneration of SO_(x)trap) through the NSR catalyst without/or with minimal poisoning of NSRcatalyst sites (e.g. Pt and BaCO₃ sites). More particularly, the methodsinclude passing the sulfur species (SO₂, H₂S) through a NSR catalystunder rich conditions at a controlled temperature window (from about 400to 575° C.), and in presence of a controlled amount of H₂. The methodsalso include passing the sulfur species (SO₂, H₂S) through the NSRcatalyst under rich conditions at a controlled temperature window (about400 to 575° C.) and controlling the molar ratio of H₂ to sulfur species(e.g. H₂/total sulfur species of about 50 or higher at 450° C.).However, this molar ratio may be lower at higher temperatures.

The methods disclosed herein for passing the sulfur species from thesulfur trap through the NSR catalyst trap are advantageous because theyresult in little to no change in NSR catalyst activity when the NSRcatalyst temperature window (e.g. about 400 to 575° C.) and molar ratioof H₂ to sulfur species are controlled. In one exemplary embodiment, thetemperature around the NSR catalyst may need to be increased if theSO_(x) trap formulation may be regenerated at a lower temperature (e.g.below 400° C.). The temperature around the NSR catalyst may be increasedeither by adding external heating or by oxidation of reductants. On theother hand, in another exemplary embodiment, when the SO_(x) trapregeneration occurs at high temperatures (e.g. >575° C.), then thetemperature around the NSR catalyst may be controlled either by using acooling system or by controlling the distance between NSR catalyst andSO_(x) trap in the exhaust pipe.

The present disclosure also relates to improvements in an exhaust gascleaning system, which operates with lean air/fuel ratios over most ofthe operating period. The exhaust gas treatment unit comprises anitrogen oxides trap (NSR) catalyst and a sulfur trap located upstreamof the nitrogen oxides trap. It has been discovered that the release ofsulfur from a SO_(x) trap as SO₂ or H₂S in presence of moderate amountsof H₂ leads to no or a minimal adsorption of sulfur on the NSR catalysttrap when compared to the release of sulfur species in the presence ofhydrocarbon (HC) and/or carbon monoxide (CO). This break-through willsignificantly improve the NSR catalyst trap lifetime and performance.This also permits sulfur regeneration to be carried out at moderatetemperature (400-600° C.). In addition, any H₂S formed will be trappedunder rich conditions, using a clean-up catalyst trap downstream of theNSR catalyst trap, and released as SO₂ during lean conditions.

The advantageous effects of incorporating a sulfur trap within theexhaust system are exhibited by monitoring the resulting improved NO_(x)adsorption efficiency. Reference made to the figures that follow showthat the NO_(x) storage over the NSR catalyst trap decreases followingthe release of sulfur species under a simulated rich exhaust containingC₃H₆/CO (see FIGS. 9, 10). On the other hand, NO_(x) storage was notaffected by the release of sulfur species in the presence of H₂ (seeFIGS. 11, 12). In view of this contrast, a further advantage of thepresent system is that the durability of a NSR catalyst trap whenpositioned downstream of a sulfur trap can be considerably increased.Another advantage includes the ability to regenerate the sulfur trap andNSR catalyst trap at a temperature below 600° C., which can avoid thethermal stress of the catalyst and the corresponding fuel penalty. Afurther advantage of the present disclosure is improved control ofhydrogen sulfide, hydrocarbons, and NH₃ emissions using a clean-upcatalyst trap located just downstream of the NSR catalyst trap. Theseand other advantages will be evident from the detailed disclosure thatfollows.

The improved exhaust gas treatment unit of the present disclosureincludes a hydrogen source, a sulfur trap (also referred to as a SO_(x)trap or sulfur oxide trap), and a nitrogen oxides trap (NSR catalysttrap). In other exemplary embodiments of the present disclosure, theimproved exhaust gas treatment system additionally includes variouscombinations of a water-gas-shift catalyst, a clean-up trap, and adiesel particulate collection system. The configuration of thesecomponents within the exhaust gas treatment unit may be varied as willbe displayed by the embodiments which follow.

The hydrogen source for input to the exhaust gas treatment system may beproduced on-board the vehicle by a variety of methods and devices orstored within a refillable reservoir on board the vehicle. An exemplarymethod of generating H₂ on-board the vehicle for input to the exhaustgas treatment system is using engine control approaches (in-cylinderinjection of excess fuel, or rich combustion). Strategies for enginecontrol employ intake throttling to lower exhaust oxygen concentration,then excess fueling is used to transition rich. For instance DelayedExtended Main (DEM) strategy uses intake throttling to lower Air/Fuelratio then the main injection duration is extended to achieve richconditions. On the other hand, a post injection involves adding aninjection event after the main injection event to achieve richoperation. Both strategies lead to the conversion of fuel to a mixtureof CO and H₂ (Brian West et al. SAE 2004-01-3023). The CO can further beconverted to H₂ and CO₂ using a WGS catalyst. Another exemplary methodconsists on-board plasmatron generation of H₂ from hydrocarbon fuels asdisclosed in U.S. Pat. No. 6,176,078. Other exemplary methods forgenerating H₂ utilize catalytic devices. For instance, H₂ can beproduced by steam reforming in which a mixture of deionized water andhydrocarbon fuel are fed to a steam reformer mounted in a combustionchamber as disclosed in U.S. Pat. No. 6,176,078. Further exemplarycatalytic devices of generating H₂ for input to the exhaust gastreatment system include, but are not limited to, autothermal reforming(ATR), pressure swing reforming (as disclosed in U.S. Patent PublicationNo. 20040170559 and 20041911166), and partial oxidation of hydrocarbonfuels with O₂ and H₂O (WO patent 01/34950). The catalytic devices alwaysproduce a mixture of CO+H₂ and a WGS catalyst is needed to convert CO toH₂ and CO₂ in presence of water. Another possibility for generating H₂is to use an electrolyzer as described in the literature (Heimrich etal. SAE 2000-01-1841). The electrolyzer produces hydrogen from thedissociation of water to hydrogen and oxygen (i.e., H₂O=H₂+1/2 O₂). Theproduced hydrogen can be injected in the exhaust system or stored underrelatively high pressure on-board the vehicle.

Another method of generating additional hydrogen in the exhaust systemis to use a water-gas-shift (WGS) catalyst to convert CO (produced bythe in-cylinder injection or by catalytic devices) in presence of waterto CO₂ and H₂ by using suitable elements and supports for such. Theoverall reaction is as follows: CO+H₂O=CO₂+H₂ whereby ΔH=−41.2 kj/mol,and AG=−28.6 kj/mol. A commonly used catalyst for the WGS reaction isCuO—ZnO—Al₂O₃ based catalyst (U.S. Pat. No. 4,308,176). However, theperformance of the catalyst to effect carbon monoxide conversion and thehydrogen yield gradually decrease during normal operations due todeactivation of the catalyst. In addition because of the sensitivity ofthis catalyst to air and condensed water, there is a reason not to usethem for an automotive fuel processing devices.

Metal-promoted ceria catalysts have been tested as water-gas-shiftcatalysts (T. Shido et al, J. Catal. 141 (1994) 105; J. T. Kummer, J.Phys. Chem. 90 (1986) 4747). The combination of ceria and platinumprovide a catalyst that is more oxygen tolerant than earlier knowncatalysts. Moreover, ceria is known to play a crucial role inautomotive, three-way, emissions-control because of its oxygen-storagecapacity (H. C. Yao et al. J. Catal. 86 (1984) 254). Deactivation of theoxygen storage capacity of ceria by high temperatures in automotiveapplications is well known, and it is necessary to stabilize thereducibility of ceria for that application by mixing it with zirconia(Shelef et al. “Catalysis by Ceria and related Materials”, ImperialCollege press, London 2002, p. 243).

The improved catalyst composition for the WGS of the present disclosureused in the shift converter comprises a noble metal catalyst having apromoting support. The support comprises a mixed metal oxide of at leastcerium oxide and zirconium oxide. The zirconia increases the resistanceof ceria to sintering, thereby improving the durability of the catalystcomposition. Additionally, alumina may be added to the catalystcomposition to improve its suitability for washcoating onto a monolithicsubstrate. An exemplary combination of catalyst element and supportmaterial of the present disclosure for a WGS catalyst is Pt supported onceria, Pt supported on ceria-zirconia, Rh supported on ceria, Rhsupported on ceria-zirconia, or combinations thereof.

The present disclosure further includes a sulfur (SO_(x)) trap upstreamof WGS catalyst to protect the WGS and the NSR trap from sulfurpoisoning under lean conditions. The release of sulfur species willoccur in the temperature range of 400-600° C. to avoid any adsorption ofsulfur species on NSR. The sulfur (SO_(x)) trap may be prepared by usingknown techniques for the preparation of vehicle exhaust gas catalysts.The sulfur trap includes a catalyst composition suitable for adsorbingSO_(x) as metal sulfate under lean (oxidative) conditions and desorbingaccumulated sulfate as SO₂ by reduction of metal sulfate under rich(reducing) conditions. The composition of the sulfur trap is furtherdesigned to prevent sulfur poisoning of after treatment devices, andespecially the NSR catalyst trap. The sulfur oxide trap elements areselected based on their ability to release sulfur at low temperatures(≦575° C.) under rich exhaust conditions.

Suitable sulfur (SO_(x)) traps are selected from oxides of copper, iron,cobalt, silver, manganese, tin, ceria, zirconia, lithium, titania andcombinations thereof. The aforementioned SO_(x) adsorbent materials maybe used as mixed metal oxides or supported on alumina, stabilized gammaalumina, silica, MCM-41, zeolites, titania, and titania-zirconia, Thesupport material may have a surface area of from 10 to 1000 m²/g, orfrom 50 to 500 m²/g, or from 100 to 400 m²/g, or from 200 to 300 m²/g.

In one form, the sulfur oxides trap is composed of a metal (M) oxide,wherein M is selected from copper, iron, manganese, cobalt, ceria,silver, zirconium and combinations thereof. Such metal oxide catalystsmay be optionally supported on a catalyst support (S) which is selectedfrom an oxide of alumina, stabilized gamma alumina with rare earthcomponents, MCM-41, zeolites, silica, magnesium, zirconia, ceria,ceria-zirconia, titania, titania-zirconia, and combinations thereof. Inthis form, the metal oxide adsorbs SO_(x) as a metal sulfate at atemperature from 200 to 600° C., or 200 to 550° C., or 200 to 500° C.under lean exhaust conditions from the combustion source. Additionally,the metal oxide then desorbs SO_(x) by reduction of metal sulfate at atemperature from 300 to 575° C., or 400 to 575° C., or 400 to 500° C.,or 500 to 550° C. under rich exhaust conditions from the combustionsource. For example, the sulfur oxides trap may include an oxide of thestructure iron oxide/support oxide wherein support is selected from thegroup consisting of Al₂O₃, SiO₂, ZrO₂, CeO₂—ZrO₂, TiO₂—Al₂O₃, MCM-41,and Zeolites. The Iron oxide system has low SOx adsorption efficiency atlow temperature (<350° C.). The low temperature SOx adsorption of thesystem can be improved by adding an upstream Pt oxidation catalyst.Alternatively, Ag and Ce may also be added to iron oxide formulation.When manganese oxide or ceria is used as the sulfur trap catalystcomposition, no upstream Pt oxidation catalyst is needed. In this form,ceria and manganese oxide adsorbs SOx as a metal sulfate at atemperature from 200 to 550° C., or 200 to 500° C. under lean exhaustconditions from the combustion source. Additionally, the manganese oxideor cerium oxide then desorbs SO_(x) as SO₂ or a mixture of SO₂ and H₂Sby reduction of metal sulfate at a temperature from 550 to 650° C., or550 to 600° C., or 550 to 575° C., or at 575° C. under a rich exhaustconditions from the combustion source.

In yet another form, the regenerable sulfur oxides trap catalystcomposition for trapping SO_(x) from a combustion source comprises ametal oxide selected from Ce—Zr oxide, Ce—Fe oxide, Ce—Zr—Fe oxide, andcombinations thereof. Such metal oxide catalysts may also be optionallysupported on a catalyst support (S) which is selected from an oxide ofalumina, stabilized gamma alumina with rare earth components, MCM-41,zeolites, silica, magnesium, zirconia, ceria, ceria-zirconia, titania,titania-zirconia, and combinations thereof. In this form, the metaloxide adsorbs SO_(x) as a metal sulfate at a temperature from 200 to600° C., or 200 to 550° C., or 200 to 500° C. under lean exhaustconditions. Additionally, the metal oxide desorbs SO_(x) by reduction ofmetal sulfate at a temperature from 300 to 575° C., or 300 to 550° C.,or 400 to 550° C. under rich exhaust conditions. In one particular form,when the catalyst composition comprises Ce—Fe oxide, SO_(x) may beadsorbed as a metal sulfate at a temperature from 200 to 600° C., or 200to 550° C. under lean exhaust conditions. Additionally, the Ce—Fe oxidedesorbs SO_(x) by reduction of metal sulfate at a temperature from 400to 575° C., or 400 to 500° C., or 450° C. under rich exhaust conditions.Silver may be further included in the catalyst composition to extendthese operating windows for adsorption and desorption.

In another form, the regenerable sulfur oxides trap catalyst compositionfor trapping SO_(x) from a combustion source comprises a mixed metal(M)-La—Zr oxide, wherein M is selected from Cu, Fe, Mn, Ag, Ce, Co andcombinations thereof. Such metal-La—Zr oxide may be optionally supportedon a catalyst support (S) which is selected from an oxide of alumina,stabilized gamma alumina with rare earth components, MCM-41, zeolites,silica, magnesium, zirconia, ceria, ceria-zirconia, titania,titania-zirconia, and combinations thereof. In this form, themetal-La—Zr oxide adsorbs SO_(x) as a metal sulfate at a temperaturefrom 200 to 600° C., or 200 to 550° C., or 200 to 500° C. under leanexhaust conditions. Additionally, the metal-La—Zr oxide desorbs SO_(x)by reduction of metal sulfate at a temperature from 300 to 650° C., or300 to 575° C., or 400 to 575° C., or 300 to 550° C., or 400 to 625° C.,or 500 to 625° C., or 500 to 600° C., or 550 to 600° C. or 550 to 575°C. under rich exhaust conditions. In one advantageous form, themetal-La—Zr oxide is a mixed Mn—La—Zr oxide. More particularly, theMn—La—Zr oxide comprises from 5 to 25 wt % Mn, from 3 to 10 wt % La,from 5 to 60 wt % Zr. The Mn—La—Zr oxide catalyst may have a samplesurface area from 50 to 400 m²/gram. These mixed metal oxides may besupported on a support material. The support material may be selectedfrom alumina, stabilized gamma alumina, MCM-41, zeolites, silicatitania, titania-zirconia, and combinations thereof. The supportmaterial may have a surface area of from 10 to 1000 m²/g, or from 50 to500 m²/g, or from 100 to 400 m²/g, or from 200 to 300 m²/g.

The sulfur trap catalyst compositions and supports disclosed hereinresult in selective oxidation of CO from the combustion source to formCO₂ while leaving H₂ unreacted (H₂O does not form) under rich exhaustconditions. The H₂ source is needed to assist in regenerating the sulfurtrap by desorbing SO_(x). Under lean conditions, SO_(x) in thecombustion source is converted to a metal sulfate through the use ofcatalyst compositions disclosed herein.

The nitrogen storage reduction (NSR) catalyst (also referred to asnitrogen oxide trap, NO_(x) trap, NO_(x) adsorbent) may be selected fromthe noble metals, including, but not limited to Pt, Pd, Rh, andcombinations thereof, and a porous carrier or substrate carrying thenoble metals, including, but not limited to alumina, MCM-41, zeolites,titania, and titania-zirconia. The NSR catalyst trap may further includealkali metals and/or alkaline earth metals, for example, Li, K, Cs, Mg,Ca, Sr, Ba and combinations of the alkali metals and alkaline earthmetals. The NSR catalyst trap may also include ceria, zirconia, titania,lanthanum and other similar materials, which are typically employed in athree-way catalyst. Ag may be included in the NSR composition whilelowering the Pt content (or removing Pt) because Ag was found to enhanceNO oxidation to NO₂ and thus NO_(x) storage efficiency. Other NSRformulations described in the literature may also be used.

For the sulfur traps disclosed herein to be effective for NSR catalystprotection, a number of critical parameters need to be controlledincluding one or more of the following: It is clear from this study thatfor sulfur trap to be a feasible system for NSR catalyst protection anumber of critical parameters need to be controlled, which are asfollows: (1) Temperature around NSR catalyst during sulfur speciesrelease from SO_(x) trap which needs to be controlled at a temperaturewindow from about 400 to 575° C., or 425 to 550° C., or 450 to 500° C.,(2) molar ratio of H₂ to sulfur species (e.g. this ratio need to beclose to about 50 and higher, or 60 and higher, or 80 and higher, or 100and higher at a temperature of 450° C., and (3) the nature of NO_(x)storage sites (e.g. keep barium sites as BaCO₃ and avoid the formationof Ba(OH)₂/BaO) and the spacing between SO_(x) trap and NSR catalystbecause it will affect the temperature around NSR catalyst. An externalunit to control the temperature window around NSR catalyst may beoptionally added if necessary. Regarding the molar ratio of H₂ to sulfurspecies, when higher temperatures are used, this ratio may decrease. Forexample, at a temperature of 500° C., the ratio may be 20 and higher, or30 and higher, or 40 and higher, or 50 and higher. In another example,at a temperature of 600° C., the ratio may be 10 and higher, or 20 andhigher, or 30 and higher, or 40 and higher.

In a further advantageous embodiment, the exhaust system according tothe disclosure includes a clean-up catalyst trap downstream of the NSR.This is particularly useful with SO_(x) traps wherein duringregeneration produce H₂S, which has an unpleasant smell. In order tocombat this, the clean-up catalyst trap comprises a component forsuppressing H₂S, for example oxides of one or more of nickel, manganese,cobalt and iron. Such components are useful at least because of theirability to trap hydrogen sulfide under rich or stoichiometric conditionsand, at lean conditions, to promote the oxidation of hydrogen sulfide tosulfur dioxide. In an alternative embodiment, the clean-up catalyst canalso be configured so as to contend with HC slip past the oxidationcatalyst of the disclosure, which can occur where there is insufficientoxygen in the gas stream to oxidize the HC to H₂O and CO₂. In this case,the clean-up catalyst includes an oxygen storage component withcatalytic activity, such as ceria and or Pt group metals (PGM). Theclean-up catalyst trap may also contain a NH₃ trap which may form duringregeneration of the NSR catalyst trap. The NH₃ trap preferably includeszeolites such as ZSM-5, Beta, MCM-68, or metal containing zeolites,wherein the metal can be selected from Fe, Co, and Cu. The trapped NH3can then react with NO_(x) to form N₂ under lean conditions. Ifnecessary, air can be injected upstream of the clean-up catalyst duringrich regeneration of the SO_(x) trap.

All the catalysts systems (catalytic H₂ generation, SO_(x) trap, NSR,WGS and clean-up catalyst) described above may be provided on a separatesubstrate such as a flow-through honeycomb monolith. The monolith may bemetal or ceramic, where ceramic it can be cordierite, although alumina,mulitte, silicon carbide, zirconia are alternatives. Manufacture ofcoated substrate may be carried out by methods known to one skilled inthe art.

A catalyzed Diesel Particulate Filter (DPF) system may be optionallypositioned (for a diesel engine) upstream of the sulfur trap to removeparticulate matter from the engine exhaust source. The DPF system isparticularly advantageous when combusting diesel fuels. A variety of DPFand filter configurations are available in the market today (Summers etal. Applied Catalysis B: 10 (1996) 139-156). The most common design ofDPF is the wall-flow monolith, which consists of many small parallelceramic channels running axially through the part (Diesel particulatetraps, wall-flow monoliths, Diesel Technology Guide atwww.dieselnet.com). Adjacent channels are alternatively plugged at eachend in order to force the diesel exhaust gases through the poroussubstrate walls, which act as a mechanical filter. As the particulate(soot) load increases and the need for regeneration increases. Theregeneration requires the oxidation of the collected particulate matter.Pt may be added to DPF to enhance such oxidation. In one form, a Ptoxidation catalyst trap may be positioned upstream of the sulfur trapwhen using iron oxide as the sulfur trap catalyst material because ofthe relatively poor adsorbing characteristics of SO_(x) at lowtemperatures (<350° C.). The use of a Pt oxidation catalyst trap alsohelps in broadening the temperature window for adsorption at lowertemperatures (<350° C.). In contrast, in another form when usingmanganese oxide or cerium oxide as the sulfur trap catalyst material, aPt oxidation catalyst trap may not be needed upstream of the sulfurtrap. Additionally, silver may be added to SO_(x) trap formulation or Ptoxidation catalyst to enhance low temperature SO_(x) adsorption.

The above systems may be organized into various configurations to yieldimproved exhaust gas treatment systems. The various configurationsinclude, but are not limited to, a series arrangement of the systems, alayered arrangement of the systems, and a combination of a series andlayered arrangement of the systems. The various configurations of theexhaust gas treatment system will be demonstrated by the exemplaryembodiments which follow.

FIG. 1 depicts an exemplary embodiment of the present disclosure for animproved exhaust gas treatment unit comprising a combustion engineexhaust source, a hydrogen generator system (1), a SO_(x) trap (2)downstream of the H₂ generator system (1), and a NSR catalyst trap (3)downstream of the SO_(x) trap (2). During the lean operation of theengine, SO₂ is oxidized to SO₃ which is trapped as sulfate on sulfurtrap (2) components. During the rich operation of the engine and at atemperature of 450° C., the sulfates are decomposed, and the releasedsulfur species pass through NSR catalyst trap (3) in the presence of H₂(1). The quantities of sulfur oxides contained in the exhaust gas froman internal combustion engine are much smaller than the quantities ofnitrogen oxides, and therefore, it is not necessary to also removesulfur from the sulfur oxide trap each time the nitrogen oxides arereleased from the storage catalyst. The period of the cycle forreleasing nitrogen oxides from the NSR catalyst trap is about oneminute, whereas the period for releasing from the sulfur trap is severalhours. The exemplary embodiment of FIG. 1 with the hydrogen generatedupstream of the sulfur trap is suitable when the hydrogen sourceoriginates from the combustion engine.

FIG. 2 depicts an alternative exemplary embodiment of a treatment unitfor an exhaust gas according to the present disclosure comprising acombustion engine exhaust source, a SO_(x) trap (2), a hydrogengenerator system (1) downstream of the SO_(x) trap (2), and a NSRcatalyst trap (3) downstream of the hydrogen generator system (1). Theonly difference from FIG. 1 is the position of the H₂ generator system(1) being positioned downstream of the SO_(x) trap (2) and upstream ofthe NSR catalyst trap (3). The exemplary embodiment of FIG. 2 with thehydrogen injected between the sulfur trap and the NSR catalyst trap isparticularly suitable when the hydrogen source originates from a sourceother than the combustion engine.

FIG. 3 depicts an alternative exemplary embodiment of an exhaust gaspurifying system for an internal combustion engine according to thepresent disclosure including a H₂ generation system (1) and 3 catalystsystems (sulfur trap (2), a water-gas-shift (WGS) catalyst (2′), and aNSR catalyst trap (3)). The H₂ generation system (1) is positioneddownstream of the engine exhaust source and upstream of the sulfur trap(2). A WGS catalyst (2′) is positioned downstream of the sulfur trap (2)and upstream of a NSR catalyst trap (3). The only difference from FIG. 1is that a WGS catalyst (2′) is added upstream of the NSR catalyst trap(3).

FIG. 4 depicts a further exemplary embodiment of an exhaust gaspurifying system for an internal combustion engine, according to thepresent disclosure, having a H₂ generator system (1), 3 catalyst systems(sulfur trap (2), a WGS catalyst (2′), a NSR catalyst trap (3)), andadditionally a clean-up catalyst (4). The H₂ generation system (1) ispositioned downstream of the engine exhaust source and upstream of thesulfur trap (2). A WGS catalyst (2′) is positioned downstream of thesulfur trap (2) and upstream of a NSR catalyst trap (3). A clean-upcatalyst (4) is then positioned downstream of the NSR catalyst trap (3).The only difference from FIG. 3 is the addition of a clean-up catalysttrap (4) downstream of the NSR catalyst trap (3).

The preceding exemplary embodiments may further include a particulateremoval system downstream of the engine exhaust source and upstream ofboth the hydrogen generation system (1) and the sulfur trap (2). Theparticulate removal system is particularly advantageous when a diffusionflame type combustion is utilized, for example as in current day dieselengines, since this leads to soot formation.

The catalyst comprising the exhaust gas treatment system may bealternatively configured in a layered arrangement by forming layers ofone of more of the various catalysts (SO_(x), WGS, NSR catalysts) on topof one another. For example, the NSR catalyst trap is deposited as acontiguous layer on a suitable support material, and then the sulfuroxide catalyst is deposited as a contiguous layer on top of the NSRcatalyst trap layer. In an alternative exemplary embodiment, the NSRcatalyst trap is deposited as a contiguous layer on a suitable supportmaterial, the WGS catalyst deposited as a contiguous layer on top of theNSR catalyst trap layer, and then the sulfur oxide catalyst deposited asa contiguous layer on top of the WGS catalyst layer. In these layeredcatalyst configurations, the exhaust gas diffuses first through theouter sulfur oxide catalyst layer, followed by the WGS catalyst layer,and finally the through NSR catalyst trap layer. These exemplary layeredcatalyst configurations are coupled with an upstream hydrogen generationsource. In addition, these exemplary layered catalyst configurations maybe optionally configured with an upstream particulate removal system,and a downstream clean-up catalyst trap.

Applicants have attempted to disclose all embodiments and applicationsof the disclosed subject matter that could be reasonably foreseen.However, there may be unforeseeable, insubstantial modifications thatremain as equivalents. While the present disclosure has been describedin conjunction with specific, exemplary embodiments thereof, it isevident that many alterations, modifications, and variations will beapparent to those skilled in the art in light of the foregoingdescription without departing from the spirit or scope of the presentdisclosure. Accordingly, the present disclosure is intended to embraceall such alterations, modifications, and variations of the abovedetailed description.

The following examples illustrate the present disclosure and theadvantages thereto without limiting the scope thereof.

Test Methods

In terms of catalyst preparation, the NSR catalyst trap used for thesestudies was supplied in washcoated monolith from a commercial source.The washcoat composition contains NO_(x) reduction sites (Pt/Rh), astorage compound (Ba), support (γ-Al₂O₃), and other promoters selectedfrom ceria, titania, zirconia and lanthanum. The catalyst was pretreatedat 450° C. for 15 minutes under simulated rich exhaust before testing(see Table 1, Feed 1).

The monolithic NSR core (0.75 in length×0.5 in diameter) is placed in aquartz reactor on top of a piece of quartz wool with several inches ofcrushed fused quartz added as a preheat zone. The quartz reactor isheated by a furnace. The temperature is controlled by a type-Kthermocouple located inside a quartz thermowell inside the narrowed exitportion of the reactor located below the monolithic core. The activitytests were conducted in a flow reactor system by using different gasmixtures as depicted in Table 1. A FTIR and a Mass Spectrometer (MS)were used to analyze the gas phase effluents (e.g., NO, NO₂, H₂S, SO₂,N₂O, NH₃, CO, CO₂, etc.). Two rich gas mixtures were considered forsulfur species adsorption on the catalyst. The first gas consists of 90ppm SO₂ (or H₂S), 2000 ppm C₃H₆, 1000 ppm CO, 11% CO₂, 6% H₂O in He(Table 1, Feed 2 a). The second gas consists of 90 ppm SO₂ (or H₂S), 1%H₂, 11% CO₂, 6% H₂O in He (Table 1, Feed 2 b). The sulfur speciesadsorbed while flowing a rich gas mixture were then oxidized under alean gas mixture (Table 1, Feed 3) before measuring NO_(x) storagecapacity of the catalyst. Tests for NO_(x) storage capacity were done at300° C. flowing a lean gas mixture containing NO (Table 1, Feed 4) overboth fresh and sulfur-poisoned NSR catalyst. After NO_(x) adsorption asnitrate, a regeneration step is used to decompose the nitrate using arich gas mixture (Feed 2 a or Feed 2 b) free of SO₂ or H₂S.

TABLE 1 Rich-lean gas mixtures used at the laboratory test experimentsOxidation Pre- of the NO_(x) treatment Sulfur adsorbed sulfur storageComponents under rich poisoning under species under under lean in theconditions rich conditions lean conditions conditions feed Feed 1 Feed2a Feed 2b Feed 3 Feed 4 SO₂ or H₂S 0 90 90 0 0 (ppm) NO (ppm) 250 250250 250 250 C₃H₆ (ppm) 2000 2000 0 2000 0 CO (ppm) 1000 1000 0 1000 0 H₂(%) 0 0 1 0 0 CO₂ (%) 11 11 11 11 11 O₂ (%) 0 0 0 7 7 H₂O (%) 6 6 6 6 0He Balance balance balance Balance balanceThe total flow rate was 3000 cc/min, which corresponds to a spacevelocity of 49,727 h⁻¹ (@ STP). The temperature was varied from 300 to600° C.

FTIR. The spectrometer used was a Nicolet 670. A liquid nitrogen cooledMCT (Hg/Cd/Te) IR detector was used to provide a high-signal-to-noiseratio. Because of the narrow natural linewidth of the small gasmolecules studied, we operated at a resolution of 0.5 cm⁻¹. At thisresolution, one scan requires 1.5 seconds. Background spectra werecollected daily, with the cell filled with flowing dry He. Two gas cellswith a path length of 2 and 10 m, equipped with ZnSe windows were used.The cell was heated to a temperature of 165° C.

Mass spectrometer. A quadrupole MS (Pfeifer vacuum system) was used forsulfur species analysis

XRD. X-ray powder diffraction patterns were recorded on a Siemens D500diffractometer using Cu Kα radiation.

Thermodynamic calculations. The thermodynamic calculations wereperformed using the commercial software HSC Chemistry.

EXAMPLES Example 1 Effect of SO₂ and H₂S on NO_(x) Reduction Efficiencyat 450° C.

The interaction of sulfur species with noble metal sites (e.g., Pt andor Rh) can directly be determined by looking to NO_(x) reduction underrich conditions. Any poisoning of noble metal sites will translate intoa decrease in NO_(x) conversion. FIG. 5 depicts a graphical illustrationof the effect of trapped SO₂ and H₂S on NO_(x) reduction at 450° C.under a simulating rich exhaust containing C₃H₆/CO (Feed 2 a). As can beseen in FIG. 5, 100% NO_(x) conversion is achieved without sulfur. Uponaddition of sulfur species (SO₂ or H₂S), NO_(x) conversion decreases asa function of exposure time. For instance, after 15 minutes of exposureto SO₂, NO_(x) conversion decreases by about 20%. This decrease reached50% in the presence of H₂S, indicating that sulfur poisoning of noblemetal sites is more severe with H₂S than with SO₂. NO_(x) conversionstabilizes at around 40%, which indicates only a partial poisoning ofthe noble metal sites. FIG. 6 depicts a graphical illustration of theeffect of SO₂ on NO_(x) reduction at 450° C. under a simulating richexhaust containing 1% H₂ (Feed 2 b). As depicted in the figure, 100%NO_(x) conversion is obtained, which shows no poisoning of noble metalsites. FIG. 7 depicts a graphical illustration of the effect of H₂S onNO_(x) reduction at 300° C. and at 450° C. under rich gas mixturescontaining H₂ (Feed 2 b). As can be seen, at 300° C. NO_(x) conversiondecreases, but stabilizes at around 50%, which again indicates thepoisoning of only a fraction of the noble metal sites. On the other handat 450° C., 100% NO_(x) conversion is obtained, showing no poisoning ofnoble metal sites. FIG. 8 depicts a graphical illustration of the effectof H₂S on NO_(x) reduction at 300° C. under rich gas mixtures containingC₃H₆/CO (Feed 2 a). As can be seen, a complete poisoning of metal sites(Pt and Rh) when the NSR catalyst trap is exposed to rich gas mixturescontaining CO/C₃H₆ and in presence of H₂S at 300° C. Indeed, NO_(x)conversion was completely lost after a 10 minute exposure to H₂S, andeven after removal of H₂S, the NO_(x) conversion was not restoredindicating irreversible poisoning of noble metal sites. However, afteraddition of 500 ppm oxygen to the rich mixture (Feed 2 a), full recoveryof NO_(x) conversion is observed indicating noble metal sitesregenerated.

The decrease in NO_(x) conversion in the presence of sulfur species(FIG. 5) is attributed to the formation of metal sulfide (e.g., PtS) dueto H₂S and SO₂ dissociation over noble metal sites. The fact that underthe conditions used NO_(x) conversion stabilizes to around 40-50% in thepresence of sulfur species (FIGS. 5, 7) indicates that a limited portionof noble metal sites are poisoned by sulfur. Based on publishedliterature, we attribute the decrease in NO_(x) conversion to thepoisoning of Pt sites, but not of Rh sites. Indeed, early laboratorystudies of Pt and Rh in three-way catalysts (TWC) showed sulfurinhibition of catalytic activity to be dependent upon both catalystcomposition and the operating conditions (W. B. Pierson et al., SAEpaper, 790942 (1979). W. B. Williamson et al., Env. Sci. Tech., 14(1980) 319. J. C. Summers and K. Baron, J. Catal., 57 (1979) 266. G. C.Joy et al. SAE paper, 790943 (1979)). It was found that SO₂ severelyinhibited NO_(x) conversion and ammonia formation over Pt under fuelrich operating conditions, but had minimal effect on the NO_(x)performance of Rh catalysts. The sulfur inhibition was found to be muchlower under stoichiometric conditions. It was also found that NO_(x)reduction over Rh is higher than over Pt, both in the presence andabsence of SO₂. The difference in performance between Rh and Pt is morepronounced when SO₂ is present due to the greater sulfur inhibition ofthe Pt catalyst (J. C. Summers and K. Baron, J. Catal., 57 (1979) 266).In the presence of CO, SO₂ was not adsorbed on the Rh catalyst, butcoadsorption of CO and SO₂ was observed on the Pt catalyst (H. S. Gandhiet al., SAE paper 780606 (1978)). These literature results reveal astronger interaction of sulfur species with Pt than with Rh. Anotherinteresting observation is that the addition of small amount of O₂ torich exhaust leads to full recovery of NO_(x) reduction (FIG. 8)indicating that sulfide species can be removed from the noble metalsurface, apparently achieved by the reverse of reaction 3 and formationof SO₃ as shown in reaction:((S)ad+3(O)ad=(SO₃)ad=(SO₃)g

One issue with adding oxygen to avoid noble metal poisoning is that theoxidation of the adsorbed sulfide species leads to the formation of SO₃which can then poison NO_(x) storage components (e.g., Ba sites).

Example 2 NO_(x) NO+NO₂) Adsorption Under Lean Conditions (Feed 3,Table 1) at 300° C. after Oxidation of Adsorbed Sulfur Species

In order to exhibit the extent that NO_(x) storage sites (e.g., Ba) arepoisoned by the trapped sulfur species, we have evaluated NO_(x) storageefficiency at 300° C. under lean conditions (Table 1, Feed 4) for afresh NSR trap and after different cycles of sulfur-poisoning. Eachcycle of poisoning consists of treating Pt-containing NO_(x) trap at 300or 450° C. with a rich gas feed containing SO₂ or H₂S (Table 1, Feed 2 aor 2 b) for 30 minutes followed by oxidation under lean conditions(Table 1, Feed 3) for 15 minutes. Any poisoning of NO_(x) storage sites(e.g., Ba) by sulfur translates into a decrease in NO_(x) storageefficiency. The NO_(x) storage was evaluated using Feed 4 (Table 1).

FIG. 9 depicts a graphical illustration of NO_(x) storage efficiency(Feed 3) at 300° C. following 1 cycle poisoning by SO₂ under simulatedrich conditions containing C₃H₆/CO (Feed 2 a) and oxidation (Feed 3) at450° C. of the adsorbed SO₂. FIG. 10 depicts a graphical illustration ofNO_(x) storage efficiency (Feed 3) at 300° C. of NSR catalyst trapfollowing 1 and 5 cycles poisoning by H₂S under simulated richconditions containing C₃H₆/CO (Feed 2 a) and oxidation (Feed 3) at 450°C. of the adsorbed H₂S between each cycles. FIG. 11 depicts a graphicalillustration of NO_(x) storage efficiency (Feed 4) at 300° C. following1 and 5 cycles poisoning by SO₂ under simulated rich conditionscontaining H₂ (Feed 2 b) and oxidation at 450° C. (Feed 3) of theadsorbed SO₂ between each cycle. FIG. 12 depicts a graphicalillustration of NO_(x) storage efficiency (Feed 4) at 300° C. following1 and 5 cycle poisoning by H₂S under simulated rich conditionscontaining H₂ (Feed 2 b) and oxidation at 450° C. (Feed 3) of theadsorbed H₂S between each cycle. FIG. 13 depicts a graphicalillustration of NO_(x) storage efficiency (Feed 4) at 300° C. following1 and 5 cycle poisoning by H₂S under simulated rich conditionscontaining H₂ (Feed 2 b) and oxidation at 450° C. (Feed 3) of theadsorbed H₂S between each cycle.

FIGS. 8-13 depict the NO_(x) storage efficiency under lean conditions(Feed 4) of the poisoned NSR catalyst trap either by SO₂ (FIGS. 9, 11)or H₂S (FIGS. 10, 12, 13). The oxidation with Feed 3 of the adsorbedsulfur species during rich conditions containing C₃H₆/CO (Feed 2 a)affects NO_(x) storage components (e.g., Ba sites) after 1 cyclepoisoning by a 12 and 20% decrease in NOx storage capacity withrespectively SO₂ (FIG. 9) and H₂S (FIGS. 10, 13). The NO_(x) storageefficiency continues to decrease after 5 cycle poisoning with H₂S (FIGS.10, 13) and a loss of 40-50% is observed in line with NO_(x) storagecomponents poisoning (e.g., formation of BaSO₄ after oxidation ofadsorbed sulfur species). On the other hand, the NO_(x) storageefficiency is not affected when NSR catalyst trap was exposed to sulfurspecies in the presence of H₂ at 450° C. (FIG. 11 and FIG. 12). Inpresence of SO₂ (FIG. 11), the NO_(x) storage capacity even after 5cycle poisoning is comparable to fresh catalyst. In the presence of H₂S(FIG. 12), no difference between fresh and poisoned catalyst after thefirst 10 minutes and only minor change is observed after that with therespect to the experimental error. Even in presence of H₂, thetemperature needs to be controlled to avoid any storage efficiency loss.Indeed, NO_(x) storage capacity decreases by 20 to 50% when the NSRcatalyst trap was exposed to H₂S in presence of H₂ at 300° C. (FIG. 13).

Example 3 Understanding Sulfur Interaction with NO_(x) Storage Sites(e.g., Ba) and NO_(x) Reduction Sites (e.g., Pt)

To understand the interaction of sulfur species with barium sites, it isimportant to determine at what conditions (rich/lean) barium sites arepoisoned by sulfur. Under rich conditions, barium sites exist mainly asbarium carbonate as indicated by XRD (FIG. 14). Thermodynamiccalculation (FIG. 15) shows that 90 ppm of SO₂ or H₂S species can passthrough barium carbonate at 450° C. without forming BaSO₃ or BaS. Hence,it can be concluded that under rich gas mixtures and a temperature of450° C., no adsorption of sulfur species on barium sites occurs. It isimportant to understand why barium carbonate sites are poisoned by thetrapped sulfur species under lean conditions. There is a correlationbetween the sulfur poisoning of noble metal sites under rich conditionsand barium sites under lean conditions. Indeed, any decrease in NO_(x)reduction efficiency in the presence of sulfur species under richconditions (see FIGS. 5, 7, 8) over a NSR catalyst trap leads to adecrease in NO_(x) storage capacity under lean conditions (see FIGS. 6,9, 10, 13). On the other hand, when 100% NO_(x) reduction is observedunder rich conditions (FIGS. 6, 7), no NO_(x) storage loss under leanconditions is observed (FIGS. 11, 12). A simple scheme to explain thepoisoning of barium and Pt sites is presented in FIG. 16. Under richconditions, (C₃H₆/CO) sulfur species interact with Pt sites forming PtSand then when switching to lean conditions, the adsorbed sulfide areoxidized to SO₃, which then reacts with the barium carbonate formingBaSO₄. To avoid the PtS formation, H₂ is needed to shift the equilibriumof the reaction of Pt+H₂S=PtS+H₂. To shift the equilibrium to the right,it is important to control the temperature and H₂ concentration. Astypified in FIG. 17, H₂/H₂S is needed to avoid PtS formation. Forinstance at 450° C., the H₂/H₂S needs to be higher than 50. The H₂/H₂Sratio decreases with increasing temperature.

In summary, this study shows that under simulated rich conditions(presence of C₃H₆ and CO, no oxygen), sulfur species were trapped on theNSR catalyst trap at temperatures from 300° C. to 450° C. Suchadsorption leads to a poisoning of noble metal sites as evidenced by adecrease of NO_(x) reduction. When switching to lean conditions, thetrapped sulfur species poison barium sites as evidenced by a decrease inNO_(x) storage capacity. Under these conditions, a sulfur trap upstreamof the commercial NSR catalyst trap is not feasible and bypassing theNSR is needed if such conditions will be used. On the other hand, thisstudy shows that sulfur adsorption under rich conditions can beminimized/or eliminated by releasing the sulfur species SO₂/H₂S in thepresence of H₂ at a temperature of 450° C. At this temperature,BaSO₃/BaS formation is unfavorable and it appears that H₂ prevents theadsorption of sulfur on Pt sites. In addition, the comparison of NO_(x)storage capacity between fresh and sulfur poisoned NSR catalyst trapshows similar trapping efficiency in line with no sulfur poisoning ofbarium sites. The implication of this finding is that the development ofa sulfur trap upstream of the commercial NSR catalyst trap is feasibleif H₂ can be provided during sulfur trap regeneration. To take advantageof these findings, strategies need to be developed to generate H₂on-board the vehicle. In addition a regenerable SO_(x) trap in thetemperature range of 400-600° C. is needed to avoid sulfur adsorption bythe NSR catalyst trap and also to limit the high temperature desulfation(>650° C.) of the catalyst.

Examples 4 to 9 Sulfur Trap Preparation, Sulfation, and RegenerationPreparation

Sulfur Trap Preparation:

The support used in this work was a commercial Al₂O₃ (with differentsurface area). The Al₂O₃ support was first calcined at 550° C. for 4hours. The dried Al₂O₃ was then impregnated with metal salts solutionselected from Fe, Cu, Mn, Ce, Co, Pt and other components. The metalcontents was varied from 0.5 to 30 wt % against 100 wt % Al₂O₃ support,respectively. Other supports such as SiO₂, ZrO₂, CeO₂—ZrO₂ and ZSM-5were also used.

Cu/Al₂O₃ catalyst (Example 4) was accomplished by the incipient methodtechnique. This technique involves the addition of an aqueous solutionof copper salt to a dry Al₂O₃ carrier until reaching incipient wetness.The concentration of the aqueous copper solution was adjusted to thedesired Cu loading. As a typical example 1.8301 grams of copper nitratehemipentahydrate (Cu(NO₃)₂*2.5H₂O was dissolved in 5.2 ml of deionizedwater. To this solution was added 5 grams of the dried Al₂O₃. The asprepared solid was mixed then dried in a vacuum oven at 80° C. andcalcined in air at 550° C. for 4 hours. The final sulfur trap containedcopper in an amount of 10 wt % per 100 wt % of Al₂O₃. The copper ispresent in the calcined sample as copper oxide.

Mn/Al₂O₃ catalyst (Example 5) was prepared in the same way as in Example4. Differently from Example 4, the Al₂O₃ was impregnated with manganesenitrate hydrate. The final sulfur trap contained manganese in an amountof 10 wt % per 100 wt % of Al₂O₃. The manganese is present in thecalcined sample as manganese oxide.

Co/Al₂O₃ catalyst (Example 6) was prepared in the same way as in Example4. Differently from Example 4, the Al₂O₃ was impregnated with cobalt(II) acetate tetrahydrate. The final sulfur trap contained cobalt in anamount of 10 wt % per 100 wt % of Al₂O₃. The cobalt is present in thecalcined sample as cobalt oxide.

Fe/Al₂O₃ catalyst (Example 7) was prepared in the same way as in Example4. Differently from Example 4, the Al₂O₃ was impregnated with iron (III)nitrate nonahydrate. The final sulfur trap contained iron in amount of10 wt % per 100 wt % of Al₂O₃. The iron is present in the calcinedsample as iron oxide.

Ce/Al₂O₃ catalyst (Example 8) was prepared in the same way as in Example4. Differently from Example 4, the Al₂O₃ was impregnated with cerium(III) nitrate hexahydrate. The final sulfur trap contained Cerium in anamount of 20 wt % per 100 wt % of Al₂O₃. The cerium is present in thecalcined sample as cerium oxide.

Pt—Fe/Al₂O₃ catalyst (Example 9) was prepared as follows: the Al₂O₃support was impregnated with an aqueous solution of platinum (II) tetraamine nitrate, dried at 80° C., then calcined in He 450° C. for 1 hour.The final sample contains 2 wt % Pt. Following these steps, the driedPt/Al₂O₃ was then impregnated by renewed immersion in aqueous solutionof iron (III) nitrate nonahydrate, dried at 80° C. and calcined at 550°C. for 4 hours in air. The calcined sample contained 2 wt % Pt and 10 wt% Fe.

An oxidation Pt/Al₂O₃ catalyst (Example 10) was prepared following asimilar procedure as Example 9. This oxidation catalyst was usedupstream system of sulfur traps described in Examples 4 through 7. Thecalcined sample contained 1 wt % Pt per 100 wt % of Al₂O₃.

Ag/Al₂O₃ catalyst (Example 11) was prepared as follows: 0.1607 grams ofsilver (I) nitrate dissolved in about 5 g of de-ionized H₂O. To thissolution 5 grams of dried alumina was added. The mixture was mixed byhand and the solid was dried at 120° C. in air for at least 4 hours. Thedried sample was then calcined in air at 500° C. for 2 hours. The Agcontent was 2 weight % per 100 wt % of Al₂O₃.

Ce—Zr/Al₂O₃ catalyst (Example 12) was prepared in the same way as inexample 4. Differently from example 4, the Al₂O₃ was impregnated withzirconyl nitrate hydrate and cerium (III) nitrate hexahydrate. The finalsulfur trap contained cerium and zirconia in an amount of 10 wt % and13% per 100 wt % of Al₂O₃. The cerium and zirconia are present in thecalcined sample as cerium oxide and zirconium oxide.

Ce—Fe/Al₂O₃ catalyst (Example 13) was prepared in the same way as inexample 4. Differently from example 4, the dried Al₂O₃ support was firstimpregnated with an aqueous solution of iron (III) nitrate nonahydrate,dried at 80° C., then calcined in air at 550° C. for 4 hours. The finalsample contains 5 wt % Fe. Following these steps, the dried Fe/Al₂O₃ wasthen impregnated by renewed immersion in aqueous solution of cerium(III) nitrate hexahydrate, dried at 80° C. and calcined at 400° C. for 2hours in air. The final sulfur trap contained cerium and iron in anamount of 5 wt % and 5% per 100 wt % of Al₂O₃.

Pt—Ba/Al₂O₃ catalyst (Example 14) was prepared as follows: the Al₂O₃support was impregnated with an aqueous solution of platinum (II)tetraammine nitrate, dried at 80° C., then calcined in He @ 450° C. for1 hour. Following these steps, the dried Pt/Al₂O₃ was then impregnatedby renewed immersion in aqueous solution of barium (II) nitrate, driedat 80° C. for 12 hours and calcined at 550° C. for 4 hours in air. Thefinal sulfur trap contained platinum and barium in an amount of 1 wt %and 10% per 100 wt % of Al₂O₃.

Examples 15 to 22 describe the synthesis of mixed metal oxides ofMn—La—Zr and Fe—La—Zr.

Mn—La—Zr (Example 15) catalyst was prepared as follows: 100.53 grams ofa 35% solution of zirconyl nitrate, 19.33 grams of a of 50% solution ofManganese (II) nitrate, and 3.51 grams of Lanthanum nitrate hexahydratewere dissolved in 275 ml of distilled water. A second solution consistedof dissolving 21.0 g of lithium hydroxide monohydrate in 250 ml ofdistilled water. Under stirring the second solution was added slowly.The pH of the final composite was adjusted to approximately 9.0 by theaddition of ammonium hydroxide or nitric acid. The resultant thickslurry was stirred at 70° C. overnight. The product formed was recoveredby filtration, washed with excess water. The solids was thenre-suspended in water acidified to pH 2.6 with nitric acid. Additionalnitric acid was added until the final pH remained >6 and <7. The solidswere then separated by filtration and dried at 80° C. under vacuum for 4days. The solid was then crushed to <60 mesh and calcined in air for 4hrs at 400° C. The final product contained 9.74% Mn, 3.79% La and 54.8%Zr as determined by ICP. The measured surface area was 267.4 m²/g.

Mn—La—Zr (Example 16) catalyst was prepared as follows: 13.75 grams of a35% solution of zirconyl nitrate, 7.775 grams of a of 50% solution ofManganese (II) nitrate, and 1.365 grams of Lanthanum nitrate hexahydrateand 78.5 grams of water were combined under stirring until dissolved. Asecond solution consisted of dissolving 21.2 g of lithium hydroxidemonohydrate in 250 ml of distilled water. These two solutions werecombined slowly with a solution of 100 ml water (pH adjusted to 9.0using the second solution). The pH of the final composite was adjustedto approximately 9.0 by the addition of ammonium hydroxide or nitricacid. The resultant thick slurry was stirred at 70° C. overnight. Theproduct formed was recovered by filtration, washed with excess water.The solids was then re-suspended in water acidified to pH 2.6 withnitric acid, additional nitric acid was added until the final pHremained >6 and <7. The solids were then separated by filtration anddried at 80 C under vacuum for 4 days. The solid was then crushed to <60mesh and calcined in air at 400° C. for 4 hours. The final productcontained 20.7% Mn, 7.6% La and 38.9% Zr as determined by ICP. Thesample surface area was 239.0 m²/g.

Mn—La—Zr (Example 17) catalyst was prepared as follows: 17.82 grams of a27% solution of zirconyl nitrate, 7.775 grams of a of 50% solution ofManganese (II) nitrate, and 1.365 grams of Lanthanum nitrate hexahydrateand 78.5 grams of water were combined under stirring until dissolved. Asecond solution consisted of dissolving 21.2 g of lithium hydroxidemonohydrate in 250 ml of distilled water. These two solutions werecombined slowly with a solution of 100 ml water (pH adjusted to 9.0using the second solution). The pH of the final composite was adjustedto approximately 9.0 by the addition of ammonium hydroxide or nitricacid. The resultant thick slurry is stirred at 70° C. overnight. Theproduct formed was recovered by filtration, washed with excess water.The solids was then re-suspended in water acidified to pH 2.6 withnitric acid, additional nitric acid was added until the final pHremained >6 and <7. The solids were then separated by filtration anddried at 80° C. under vacuum for 4 days. The solid was then crushed to<60 mesh and calcined in air at 400° C. for 4 hours. The final productcontained 19.1% Mn, 7.05% La and 41.7% Zr as determined by ICP. Thesample surface area was 250.6 m²/g.

Mn—La—Zr (Example 18) catalyst was prepared as follows: 17.82 grams of a35% solution of zirconyl nitrate, 3.89 grams of a of 50% solution ofManganese (II) nitrate, and 1.365 grams of Lanthanum nitrate hexahydrateand 78.5 grams of water were combined under stirring until dissolved. Asecond solution consisted of dissolving 21.2 g of lithium hydroxidemonohydrate in 250 ml of distilled water. These two solutions werecombined slowly with a solution of 100 ml water (pH adjusted to 9.0using the second solution). The pH of the final composite was adjustedto approximately 9.0 by the addition of ammonium hydroxide or nitricacid. The resultant thick slurry was stirred at 70° C. overnight. Theproduct formed was recovered by filtration, washed with excess water.The solids was then re-suspended in water acidified to pH 2.6 withnitric acid, additional nitric acid was added until the final pHremains >6 and <7. The solids were then separated by filtration anddried at 80° C. under vacuum for 4 days. The solid was then crushed to<60 mesh and calcined in air at 400 C for 4 hours. The final productcontained 10.7% Mn, 7.74% La and 50.04% Zr as determined by ICP. Thesample surface area was 256.0 m²/g.

Mn—La—Zr (Example 19) catalyst was prepared as follows: 17.82 grams of a35% solution of zirconyl nitrate, 2.60 grams of a of 50% solution ofManganese (II) nitrate, and 1.365 grams of Lanthanum nitrate hexahydrateand 78.5 grams of water were combined under stirring until dissolved. Asecond solution consisted of dissolving 21.0 g of lithium hydroxidemonohydrate in 250 ml of distilled water. These two solutions werecombined slowly with a solution of 100 ml water (pH adjusted to 9.0using the second solution, Temperature adjusted to 70° C.). The pH ofthe final composite was adjusted to approximately 9.0 by the addition ofammonium hydroxide or nitric acid. The resultant thick slurry wasstirred at 70° C. overnight. The product formed was recovered byfiltration, washed with excess water. The solids was then re-suspendedin water acidified to pH 2.6 with nitric acid, additional nitric acidwas added until the final pH remained >6 and <7. The solids were thenseparated by filtration and dried at 80° C. under vacuum for 4 days. Thesolid was then crushed to <60 mesh and calcined in air at 400° C. for 4hours. The final product contained 8.17% Mn, 8.7% La and 50.7% Zr asdetermined by ICP. The sample surface area was 247.8 m²/g.

Mn—La—Zr (Example 20) catalyst was prepared as follows: 17.82 grams of a35% solution of zirconyl nitrate, 3.89 grams of a of 50% solution ofManganese (II) nitrate, and 1.365 grams of Lanthanum nitrate hexahydrateand 78.5 grams of water were combined under stirring until dissolved. Asecond solution consisted of dissolving 31.25 grams of ammoniumhydroxide in 250 ml of distilled water. These two solutions werecombined slowly with a solution of 100 ml water (pH adjusted to 9.0using the second solution, temperature adjusted to 70° C.). The pH ofthe final composite was adjusted to approximately 9.0 by the addition ofammonium hydroxide or nitric acid. The resultant thick slurry wasstirred at 70° C. overnight. The product formed was recovered byfiltration, washed with excess water. The solids were then re-suspendedin water acidified to pH 2.6 with nitric acid, additional nitric acid isadded until the final pH remains >6 and <7. The solids were thenseparated by filtration and dried at 80° C. under vacuum for 4 days. Thesolid was then crushed to <60 mesh and calcined in air at 400° C. for 4hours. The final product contained 9.74% Mn, 3.79% La and 54.8% Zr asdetermined by ICP. The sample surface area was 252.4 m²/g.

Fe—La—Zr (Example 21) catalyst was prepared as follows: 17.82 grams of a35% solution of zirconyl nitrate, 17.55 grams of Iron (III) nitratehydrate, and 1.365 grams of Lanthanum nitrate hexahydrate and 86.25grams of water were combined under stirring until dissolved. A secondsolution consisted of dissolving 21.2 g of lithium hydroxide monohydratein 250 ml of distilled water. These two solutions were combined slowlywith a solution of 100 ml water (pH adjusted to 9.0 using the secondsolution). The pH of the final composite was adjusted to approximately9.0 by the addition of ammonium hydroxide or nitric acid. The resultantthick slurry was stirred at 70° C. overnight. The product formed wasrecovered by filtration, washed with excess water. The solids were thenre-suspended in water acidified to pH 2.6 with nitric acid, additionalnitric acid was added until the final pH remained >6 and <7. The solidswere then separated by filtration and dried at 80° C. under vacuum for 4days. The solid was then crushed to <60 mesh and calcined in air at 400°C. for 4 hours. The final product contained 32.1% Fe, 5.65% La and 29.8%Zr as determined by ICP. The sample surface area was 194.4 m²/g.

Fe—La—Zr (Example 22) catalyst was prepared as follows: 17.82 grams of a35% solution of zirconyl nitrate, 10.11 grams of copper (II) nitratehydrate, and 1.365 grams of Lanthanum nitrate hexahydrate and 86.25grams of water were combined under stirring until dissolved. A secondsolution consisted of dissolving 21.2 g of lithium hydroxide monohydratein 250 ml of distilled water. These two solutions were combined slowlywith a solution of 100 ml water (pH adjusted to 9.0 using the secondsolution). The pH of the final composite was adjusted to approximately9.0 by the addition of ammonium hydroxide or nitric acid. The resultantthick slurry was stirred at 70° C. overnight. The product formed wasrecovered by filtration, washed with excess water. The solids were thenre-suspended in water acidified to pH 2.6 with nitric acid, additionalnitric acid was added until the final pH remained >6 and <7. The solidswere then separated by filtration and dried at 80° C. under vacuum for 4days. The solid was then crushed to <60 mesh and calcined in air at 400C for 4 hrs. The final product contained 33.9% Cu, 2.61% La and 33.4% Zras determined by ICP. The sample surface area was 110.3 m²/g.

Sulfation (SOx Trapping):

The sulfur trap catalysts from examples 4 through 9 and 12 through 22were tested in a bench flow reactor with a simulated lean exhaust gasescontaining SO₂. The simulated lean exhaust gas contained 30 ppm (or 300ppm) SO₂, 5% H₂O, 5% CO₂, 10% O₂ and the balance He at a gas hourlyspace velocity of 60,000/hr. The higher than typical sulfur dioxideconcentration, 30 ppm or 300 ppm, is utilized to accelerate thesulfation. The total flow rate of the gas was 1025 ml/minute. Typically0.5 grams of catalysts (14-25 mesh size) from examples 4 through 9 and12 through 22 was loaded in a quartz reactor then temperature heatingwas increased from 25° C. to 550° C. at 10° C./min under 10% O₂; holdingsample for 1 hour at 550° C.; cooling to the desired sulfationtemperature in the range of 200 to 500° C. At the desired temperaturethe simulated lean exhaust feed containing SO₂ was then passed throughthe catalyst for 20 hrs (with 30 ppm SO2) or for 2 hours (with 300 ppmSO2) and then the catalyst was purged with 10% O₂ in helium for 30 minthen cooled to room temperature. For comparison, the Pt/Al₂O₃ oxidationcatalyst (Example 10) was placed upstream of the sulfur traps ofExamples 4 through 8. The layered catalysts were then sulfated at thesame conditions (see above). In the case of the combination catalyst,0.25 g of the Pt/alumina catalyst was placed on top of 0.25 g of theselected SOx trap.

Regeneration of Sulfated SOx Traps:

Regeneration of sulfated SO_(x) traps was accomplished with 10% H₂+5%CO₂+5% H₂O in a He carrier gas in the same bench flow reactor at desiredtemperature or using a TGA balance where the decomposition products wereanalyzed by a Mass spectrometer (MS) system. The sulfated sulfur traps(see sulfation procedure above) were regenerated in a 10% H₂ in He.Also, a thermal decomposition of the metal sulfate was performed in He.Approximately 20 mg of the sulfated sample was placed on the TGA balance(TGA/SDTA 851, Mettler Toledo, Inc.) and the gas feed (H₂ in He or He)was passed through the sample while the temperature was increased from30° C. to 800° C. at a temperature ramp rate of 10° C./min. The sulfurspecies released from the sulfated sample were analyzed by on-line MassSpectrometer (Pfeiffer Vacuum System).

FIG. 18 shows the first derivative of the weight loss (as determined byTGA) during reduction of metal sulfate (e.g., sulfation at 400° C.). Ascan be seen, different maxima of the weight loss are observed fordifferent metal sulfate. For instance, the maximum temperature weightloss is observed at 300° C. for Cu/Al₂O₃, at 460° C. for Fe/Al₂O₃, at520° C. for Co/Al₂O₃, and at 620° C. for Mn/Al₂O₃. The MS signal of thereleased sulfur species (SO₂: m/e=64 and H₂S: m/e=34) corresponding tothis weight loss under H₂ are shown in FIGS. 19-22. As can be seen, theSO₂ was the major product of sulfur reduction. For Cu/Al₂O₃ sample, onecan see two peaks of SO₂ release at 300° C. and 350° C. Also, the H₂Sdesorption peak is observed at high temperature (>450° C.) (FIG. 19).For Fe/Al₂O₃, a single SO₂ desorption peak is observed at 460° C. and acomplete desorption below 500° C. (FIG. 20). For Co/Al₂O₃, a singledesorption peak for SO₂ is observed at max temperature of 520° C. (FIG.21). In addition, H₂S was also observed at high temperature (>600° C.).For Mn/Al₂O₃, the maximum SO₂ desorption peak can be seen at 625° C.with a complete desorption at temperature of 650° C. (FIG. 22).

The regeneration of sulfated Ce/Al₂O₃ of example 8 (sulfation at 200°C.) in 10% H₂ in He leads to two desorption peaks of SO₂ (at 580° C.)and H₂S (at 630° C.) as shown in FIG. 23. With controlling thetemperature below 600° C. it will be possible to avoid H₂S emissions.

The regeneration of the sulfated Pt—Fe/Al₂O₃ of example 9 (sulfation at400° C.) under 10% H₂ in He shows no desorption of sulfur species attemperatures below 600° C. and only H₂S is observed at temperaturehigher than 650° C. (FIG. 24). On the other hand, when H₂ is replacedwith He, the sulfate decomposition from the sulfated sample occurs inthe temperature range of 400-650° C. (FIG. 25). The sulfur is releasedmainly as SO₂. These results clearly indicate that under H₂ flow, thesulfur is retained on the catalyst. In the presence of Pt, the sulfateis reduced to H₂S which then can react with iron to form stable ironsulfide (e.g., FeS). In conclusion, it is important to keep sulfur trapsfree from Pt. One way to take advantage of the Pt is to use it as anupstream oxidation catalyst with a downstream Pt free sulfur trap(layered catalysts) selected from Examples 4 through 7. In this case theoxidation of SO₂ to SO₃ occurs upstream of sulfur trap withoutinfluencing the desorption of sulfur species from sulfur traps. Astypical examples, FIGS. 26-27 show sulfur species release from thesulfated Fe/Al₂O₃ catalyst (sulfation done with an upstream Pt/Al₂O₃from Example 10). Only one desorption peak is observed at maximumtemperature of 460° C. (FIG. 26). Also when an isothermal temperaturewas used (450° C.) a complete desorption of sulfur as SO₂ occurs and nosulfur desorption is observed when the temperature was increased from450° C. to 700° C., indicative of complete sulfur desorption from ironat 450° C. (FIG. 27).

FIG. 28 shows sulfur species desorption from a sulfated Pt—Ba/Al₂O₃ ofexample 14 (catalyst sulfated at 400° C. using 30 ppm SO₂). As can beseen the sulfur desorption occurs at a broad temperature range with H₂Sas the main product. This is not a practical trap as it will requirelong regeneration period. In addition the emission of large H₂S is notdesired.

FIG. 29 shows sulfur species desorption from a sulfated Ce—Fe/Al₂O₃ ofexample 13 (catalyst sulfated at 200° C. using 30 ppm SO₂). As can beseen the sulfur desorption occurs mainly as SO₂ at 460° C. H₂S forms athigh temperatures. It is very important to point out that ceria additionimprove significantly low temperature SO_(x) adsorption.

FIG. 30 shows sulfur species desorption from a sulfated Ce—Zr/Al₂O₃ ofexample 12 (catalyst sulfated at 200° C. using 30 ppm SO₂ for 24 hours).As can be seen the sulfur desorption occurs as a mixture of SO₂ and H₂Sin the temperature range of 500-650° C. It is very important to pointout that ceria addition improve significantly low temperature SO_(x)adsorption. The main issue is H₂S releases at high temperatures.

Metal oxide based on Mn—La—Zr formulations (examples 15 through 20) showexcellent SOx adsorption at a broad temperature window (200-500° C.). Asa typical example FIGS. 31 and 32 show SO_(x) desorption from a sulfatedMn—La—Zr of example 15 (catalyst sulfated using 300 ppm SO₂ at 200° C.:FIG. 31 and at 400° C.: FIG. 32). As can be seen sulfur is releasedmainly as SO₂. In both cases the total sulfur retained on the catalystwas around 2 wt % indicating that the system is efficient in trappingSO_(x) at 200° C. and 400° C. Similar results were obtained with otherformulations. For instance, Mn—La—Zr of example 16 sulfated at 200° C.(FIG. 33) or at 400° C. (FIG. 34) shows again that during regenerationsulfur is mainly released as SO₂ at 600° C.

Durability of SO_(x) Traps:

The as prepared SO_(x) traps were first steamed at 600° C. for 24 hrs ina bench flow reactor with simulated exhaust gas. The simulated exhaustgas contained 10% H₂O, 9% O₂, the balance He. Then the steamed SO_(x)traps were sulfated and regenerated at the desired temperature. Theprocess of sulfation/regeneration was then repeated for many cycles.Table 1 shows sulfur capacity of selected SO_(x) traps before and afteraging (steaming followed by multiple cycle of regeneration/sulfation).The first trap was Fe/Al₂O₃ of example 7 in combination with an upstreamPt/Al₂O₃ catalyst of example 10 and the second trap was Mn—La—Zr trap.The sulfation for both system was done at 400° C. (with 300 ppm SO₂+5%H₂O+5% CO₂ and 10% O₂, the balance helium for 2 hours) while theregeneration (with 10% H₂+5% CO₂+5% H₂O+He for 20 min) was done atdifferent temperatures. For Fe/Al₂O₃ the regeneration was done at 500°C. while with Mn—La—Zr the regeneration was done at 600° C. As can beseen from Table 2 only minor capacity loss was observed after multiplecycles of regeneration/sulfation. Fresh steamed Fe/Al₂O₃ adsorbs 1.9Wt-% S and after 100 cycles (about 100,000 miles) ofregeneration/sulfation the catalyst adsorbs about 1.7 wt-% S indicatingminor trapping efficiency loss (about 10%). On the other hand, a freshsteamed Mn—La—Zr sulfur capacity was 2.0 wt-% S and after 6 cycles ofregeneration/sulfation the trap capacity was 1.9 wt-% S. It is veryimportant to point out that these traps are fully regenerated and SO₂was the main product.

TABLE 2 Durability of selected SOx traps after multiple cycles ofregeneration/sulfation S capacity S capacity after after multiple cyclessteaming of regen/sulfation Cycle of SO_(x) traps (Wt-% S) (Wt-% S)regen/sulfation Fe/Al₂O₃* 1.9 1.7 100 cycles (example 2) (100,000miles)** Mn—La—Zr 2.0 1.9 6 cycles*** (example (6,000 miles)** 11)*Pt/Alumina of example 10 was used in an upstream position of Fe/Al2O3(layered catalyst) **Miles calculated based on 15 ppm S fuel ***Numberof cycles set by time available for testing not by an observedlimitation

In summary, Cu/Al₂O₃ and Fe/Al₂O₃SO_(x) trap systems are excellentcandidates for low temperature regeneration. Both systems release sulfurmainly as SO₂ with a full regeneration below 400° C. for Cu/Al₂O₃ and450° C. for Fe/Al₂O₃. It is important to note that Pt-containingcatalyst (e.g. Pt/Al₂O₃) is needed to improve low temperature (<350° C.)SO_(x) trapping efficiency of Fe and Cu-containing catalysts. Pt/Al₂O₃enhances SO₂ oxidation to SO₃ and thus SO_(x) trapping efficiency. Onthe other hand, the use of an upstream oxidation catalyst will alsoimprove NO_(x) storage efficiency of NSR catalyst because of theoxidation of NO to NO₂. Another other option is to use Ag as part of theSO_(x) trap or NSR catalyst formulations to enhance both NO and SO₂oxidation. However, with Ag-containing catalyst a small concentration ofH₂ is needed during lean condition. As a typical example, FIG. 35 showshigh NO_(x) storage capacity over Ag/Al₂O₃ catalyst when feeding 500 ppmNO+2000 ppm H₂+9% CO₂+5% H₂O at a temperature of 200° C. and a GHSV of30,000 h⁻¹. About 98% NO_(x) storage efficiency is obtained within a 1minute period. The NO_(x) are stored as nitrates on both Ag and Aluminasupport sites. It's very important to mention that a small amount of H₂is needed to reach this high NO_(x) storage because under such conditionAg will enhance NO oxidation to NO₂.

Other findings associated with the Pt/Al₂O₃ oxidation catalyst ofexample 10 is the ability of this catalyst to oxidize selectively COwhile H₂ oxidation did not take place when a rich feed contains aresidual concentration of O₂ (about 0.5 volume %). This is an importantfinding because H₂ is needed downstream of the oxidation catalyst forNSR catalyst protection from sulfur poisoning. As an illustration, FIG.36 shows the oxidation of H₂ to H₂O in presence and in the absence of COunder a rich condition containing 0.5% O₂. As can be seen in the absenceof CO, H₂ is oxidized to H₂O. On the other hand, in presence of CO, nowater is detected in line with no oxidation of H₂. The Pt/Al₂O₃ catalystoxidizes selectively CO.

For Ce and Mn containing SOx traps were found to trap efficiently SO_(x)at a broad temperature window (200-500° C.) and an upstream oxidationcatalyst is not needed. In the case of Ceria-containing formulationswere found to release sulfur as a mixture of SO₂ and H₂S. On the otherhand, Mn-containing formulation (e.g. Mn—La—Zr mixed metal oxides)releases sulfur mainly as SO2 with a full regeneration at 600° C. Thesetraps are excellent candidates for high temperature application.

For exhaust automobile application these SO_(x) trap materials can beprovided on a separate substrate such as a flow-through honeycombmonolith. The monolith can be metal or ceramic, where ceramic it can becordierite, although alumina, mulitte, silicon carbide, zirconia arealternatives. Manufacture of coated substrate can be carried out bymethods known to the skilled in the art and no further explanation willbe given here.

Examples 22-23 Water Gas Shift Catalyst Preparation and Pretreatment forCeO₂—ZrO₂ Supports

2.6% CeO₂—ZrO₂ Sample (Example 22).

Five hundred grams of ZrOCl₂.8H₂O and fourteen grams of Ce(SO₄)₂ weredissolved while stirring in 3.0 liters of distilled water. Anothersolution containing 260 grams of concentrated NH₄OH and 3.0 liters ofdistilled water was prepared. These two solutions were combined at therate of 50 ml/min using a nozzle for mixing. The pH of the finalcomposite was adjusted to approximately 8 by the addition ofconcentrated ammonium hydroxide. This slurry was then put inpolypropylene bottles and placed in a steambox (100° C.) for 72 hours.The product formed was recovered by filtration, washed with excesswater, and stored as a filtercake. The filtercake was dried overnight at100° C. Thereafter a portion of the dried filtercake was calcined at700° C. for a total of 3 hours in flowing air and then allowed to cool.The cerium content was 2.6%. Sample nomenclature was 2.6% CeO₂—ZrO₂.

17.65% CeO₂—ZrO₂ Sample (Example 23). Five hundred grams of ZrOCl₂.8H₂Oand one hundred and forty grams of Ce(SO₄)₂ were dissolved whilestirring in 3.0 liters of distilled water. Another solution containing260 grams of concentrated NH₄OH and 3.0 liters of distilled water wasprepared. These two solutions were combined at the rate of 50 ml/minusing nozzle mixing. The pH of the final composite was adjusted toapproximately 8 by the addition of concentrated ammonium hydroxide. Thisslurry was then put in polypropylene bottles and placed in a steambox(100° C.) for 72 hours. The product formed was recovered by filtration,washed with excess water, and stored as a filtercake. The filtercake wasdried overnight at 100° C. Thereafter a portion of the filtercake wascalcined at 700° C. for a total of 3 hours in flowing air. The ceriumcontent was 17.6%. Sample nomenclature was 17.65% CeO₂—ZrO2.

Testing of the WGS was done using stainless steel laboratorymicroreactors. The catalyst (25-30 mesh size) was loaded in the reactorand then reduced in 4% H₂ in helium at 400° C. for 2 hours before theWGS reaction. Water was then fed to the evaporator (at 120° C.). Thenmixed in the evaporator with the carbon monoxide (CO) and nitrogen (N₂)feed gas. The gas mixture passed into the fixed bed laboratorymicroreactor via heated lines (110° C.). Gaseous products (CO₂, H₂) fromthe reactor were quantified using the thermal conductivity detector(TCD) of a Hewlett Packard 6890 gas chromatograph. The gas mixtureconsisting of the following: CO=4%, H₂O=17% and a total flow rate suchthat the GHSV=14,638 h⁻¹.

CeO₂—ZrO₂ catalysts were inactive for the WGS reaction in thetemperature range of 150-450° C.

Examples 24 and 25 Water Gas Shift Catalyst Preparation for Pt Supportedon CeO₂—ZrO₂

2.6% CeO₂—ZrO₂ and 17.6% CeO₂—ZrO₂ supports prepared in Example 22 and23 were loaded with Pt as follows: 51 mg of the tetraammineplatine (II)chloride hydrate was dissolved in 30 ml of water, and then 3 g of theCeO₂—ZrO₂ were added. The mixture was stirred for 4 hours. The pH of thesolution was 2.41 with the 2.6% CeO₂—ZrO₂ while this value reached 2.83when 17.6% CeO₂—ZrO₂ was used. The excess solution was removed byheating at 90° C. while stirring. After drying in an oven overnight thesolids were calcined at 400° C. for 4 hours in air. The Pt loading inthe samples was 1 wt %.

The Pt/2.6% CeO₂—ZrO₂ (Example 24) and Pt/17.6% CeO₂—ZrO_(2 (Example)25) were reduced at 400° C. in 4% H₂ in He then tested for their WGSperformance at different temperatures and a total flow rate such thatthe GHSV=14, 638 h⁻¹ (FIG. 37), or at a GHSV of 73, 194 h⁻¹ (FIG. 38).As can be seen, from FIGS. 37 and 38 the catalysts are active at a broadtemperature window. At the temperature below 350° C., Pt/2.6% CeO₂—ZrO₂shows a high H₂ production than the Pt/17.6% CeO₂—ZrO₂ indicating theimportance of cerium loading in controlling the acidity of the supportand Pt dispersion. Increasing the GHSV lead to a decrease in the WGSactivity in both catalysts. At the temperature of interest to ourapplication (e.g., 450° C.), the H₂ produced is in the range 2.3-2.6%with a CO conversion in the range of 60-70%.

Examples 26 and 27 Water as Shift Catalyst Preparation and Testing of RhSupported on CeO₂—ZrO₂ Catalysts

2.6% CeO₂—ZrO₂ and 17.6% CeO₂—ZrO₂ supports prepared in Examples 22-23were loaded with Rh as follows 37.5 mg of Rhodium (III) trichloride weredissolved in 30 ml water then 3 g of the CeO₂—ZrO₂ were added. Themixture was stirred for 4 hours. The pH of the solution was 2.25 withthe 2.6% CeO₂—ZrO₂ (Example 22), and this value reached 2.58 when 17.6%CeO₂—ZrO₂ (Example 23) was used. The excess solution was removed byheating at 90° C. while stirring. After drying at 80° C. in an ovenovernight, the solid was calcined at 400° C. for 4 hours in air. The Rhloading in the samples was 0.5 wt %.

The as prepared catalysts were reduced in 4% H₂ in He at 400° C. thentested for their WGS performance in a gas mixture consisting of: CO=4%,17% H₂O and a total flow rate such that the GHSV=14,638 h⁻¹ (FIG. 39).As can be seen, both catalysts show comparable activity with a maximumH₂ concentration at around 2.5% at 450° C. and with a CO conversion of70%.

The WGS catalyst can be provided on a separate substrate such as aflow-through honeycomb monolith. The monolith can be metal or ceramic,where ceramic it can be cordierite, although alumina, mulitte, siliconcarbide, zirconia are alternatives. Manufacture of coated substrate canbe carried out by methods known to the skilled in the art and no furtherexplanation will be given here. In other embodiment the WGS componentscan be included in NSR catalyst trap formulation. Also, the WGScomponents can be layered with the NSR components on the same monolith.

Examples 28 and 29 Durability of NSR Catalyst after Multiple Cycles ofSulfur Poisoning Under H2 Rich Conditions

FIGS. 40 and 41 depict the NO_(x) storage efficiency (Feed 4, Table 1)measured at 300° C. (FIG. 40) and 450° C. (FIG. 41) over a NSR catalystafter multiple cycle of SO₂ poisoning under H₂ rich conditions at 450°C. for 20 min. (feed 2 b, table 1). As can be seen, a high NO_(x)storage efficiency (Average NO_(x) storage ≧90% for 1 min period) ismeasured even after 100 cycles of SO₂ poisoning (FIG. 40) indicatingthat passing SO₂ through NSR catalyst does not affect low temperatureNO_(x) storage sites (e.g. BaCO₃) in line with minimal poisoning ofthese sites. On the other hand, the measured NO_(x) storage at 450° C.(FIG. 41) decreases by about 50% after 100 cycles of SO₂ poisoningindicating that a part of storage sites responsible for high temperatureNO_(x) adsorption are partially poisoned by sulfur. It is very importantto mention that 1 cycle poisoning by SO₂ under lean conditions at 450°C. for 20 min. using a similar amount of SO₂ (feed 3 with 90 ppm SO₂,Table 1) leads to a loss of more than 80% NO_(x) storage efficiency(measured average NO_(x) storage for 1 min, was only 18%, FIG. 41). Itis clear from this study that for sulfur trap to be a feasible systemfor NSR catalyst protection a number of critical parameters need to becontrolled, which are as follows: (1) Temperature around NSR catalystduring sulfur species release from SO_(x) trap which needs to becontrolled at a temperature window from about 400 to 575° C., or 425 to550° C., or 450 to 500° C., (2) molar ratio of H₂ to sulfur species(e.g. this ratio need to be close to about 50 and higher, or 60 andhigher, or 80 and higher, or 100 and higher at a temperature of 450° C.,and (3) the nature of NO_(x) storage sites (e.g. keep barium sites asBaCO₃ and avoid the formation of Ba(OH)₂/BaO) and the spacing betweenSO_(x) trap and NSR catalyst because it will affect the temperaturearound NSR catalyst. An external unit to control the temperature windowaround NSR catalyst may be optionally added if necessary. Regarding themolar ratio of H₂ to sulfur species, when higher temperatures are used,this ratio may decrease. For example, at a temperature of 500° C., theratio may be 20 and higher, or 30 and higher, or 40 and higher, or 50and higher. In another example, at a temperature of 600° C., the ratiomay be 10 and higher, or 20 and higher, or 30 and higher, or 40 andhigher.

What is claimed is:
 1. A method for improving the treatment of exhaustgas comprising the steps of: i) providing a combustion source with anexhaust gas cleaning system comprising: a) a H₂ rich gas generatorsystem, b) a regenerable sulfur oxides trap, and c) a regenerablenitrogen storage reduction (NSR) catalyst trap, wherein the sulfuroxides trap comprises a catalyst selected from oxide of Fe, Co, Ag, Cu,Mn, Ce, Ce—Zr, Ce—Fe, Mn—La—Zr, Fe—La—Zr, Cu—La—Zr, Co—La—Zr Pt—Ba, Pt,and combinations thereof, and wherein the NSR catalyst trap ispositioned downstream of the sulfur oxides trap and the H₂ rich gasgenerator system, ii) regenerating the sulfur oxides trap and the NSRcatalyst trap with the H₂ rich gas and a fuel rich fuel to air exhaustgas, and iii) maintaining the NSR catalyst trap at a temperature of fromabout 400 to about 600° C. in the presence of H₂ from the H₂ rich gasgenerator system at an atomic ratio of H₂ to the released sulfur atomspecies of greater than or equal to about 65 during regeneration of thesulfur oxides trap, wherein the sulfur atom species released by thesulfur oxides trap pass through the NSR catalyst trap with no poisoningof the NO_(x) storage and NO_(x) reduction components.
 2. The method ofclaim 1, wherein the sulfur oxides trap further comprises a supportmaterial selected from an oxide of alumina, stabilized gamma aluminawith rare earth components, MCM-41, zeolites, silica, magnesium,zirconia, ceria, ceria-zirconia, titania, titania-zirconia, andcombinations thereof.
 3. The method of claim 2, wherein the sulfuroxides trap adsorbs SO_(x) as a metal sulfate at a temperature from 200to 600° C. under lean exhaust conditions.
 4. The method of claim 3,wherein the sulfur oxides trap desorbs the trapped metal sulfate byreduction at a temperature from 300 to 575° C. under rich exhaustconditions.
 5. The method of claim 4, wherein the sulfur oxides trap isa mixed Mn—La—Zr oxide, wherein the sulfur oxides trap desorbs thetrapped metal sulfate by reduction at a temperature from 500 to 575° C.under a H₂ rich exhaust conditions.
 6. The method of claim 2, whereinthe support material is alumina.
 7. The method of claim 3 wherein thesulfur oxides trap is a Fe oxide supported on alumina, wherein thesulfur oxides trap desorbs the trapped metal sulfate by reduction at atemperature from 400 to 500° C. under H₂ rich exhaust conditions.
 8. Themethod of claim 1, wherein the Mn—La—Zr oxide catalyst comprises from 1to 25 wt % Mn, from 1 to 10 wt % La, from 1 to 60 wt % Zr, and theremaining wt % oxygen.
 9. The method of claim 8, wherein the Mn—La—Zroxide catalyst has a sample surface area from 50 to 400 m²/gram.
 10. Themethod of claim 9, wherein the Mn—La—Zr oxide is supported on aluminasupport in an amount of from 1 to 90 wt %.
 11. The method of claim 1,wherein the Fe oxide is supported on an alumina support in an amount offrom 1 to 20 wt %.
 12. The method of claim 11, wherein the aluminasupport has a surface area of from 50 to 500 m²/g.
 13. The method ofclaim 1, further comprising a clean-up catalyst trap positioneddownstream of the NSR catalyst trap.
 14. The method 13, wherein theclean-up catalyst trap adsorbs hydrogen sulfide in a rich fuel to airratio condition and releases SO₂ in a lean fuel to air ratio condition.15. The method of claim 14, wherein the clean-up catalyst trap comprisesa base metal oxide selected from iron oxide, nickel oxide, manganeseoxide, silver oxide, cobalt oxide, and combinations thereof.
 16. Themethod of claim 15, wherein the base metal oxide is supported on amaterial selected from alumina, stabilized gamma alumina, MCM-41,zeolites, titania, titania-zirconia, and combinations thereof.
 17. Themethod of claim 13, wherein the clean-up catalyst trap comprisescomponents for HC/CO oxidation selected from ceria, silver, a platinumgroup metal, and combinations thereof.
 18. The method of claim 17,wherein the components for HC/CO oxidation are supported on a materialselected from alumina, stabilized gamma alumina, MCM-41, zeolites,titania, titania-zirconia, and combinations thereof.
 19. The method ofclaim 13, wherein the clean-up catalyst comprises components for NH₃trapping selected from acidic metal oxides, zeolites, andmetal-containing zeolites.
 20. The method of claim 19, wherein theacidic metal oxides are selected from tungsten-zirconia, sulfatedzirconia, sulfated ceria-zirconia, phosphated zirconia, and phosphatedceria zirconia.
 21. The method of claim 20, wherein the zeolites areselected from ZSM-5, Beta, MCM-68, Faujasite, and MCM-41.
 22. The methodof claim 19, wherein the metal-containing zeolites comprise a metalselected from copper, iron, cobalt and silver.
 23. The method of claim1, wherein a catalyzed diesel particulate filter is positioned upstreamof the sulfur oxides trap.
 24. The method of claim 1, wherein the stepof regenerating the sulfur trap catalyst trap and the NSR catalyst trapwith a fuel rich air/fuel ratio is in presence of a low concentration ofH₂ at a temperature of from about 300 to 575° C.
 25. The method of claim1, wherein the combustion source is a lean-burn engine of a vehicle.